When 24-year-old William Hurley called his girlfriend the night of October 8th, 2009, all he wanted was to go home. The Navy veteran, who’d been attending a Boston Bruins home game, asked Claire Mahoney to pick him up early, explaining that he was tired from a long day of work as a greenskeeper. While on the phone with Mahoney, Hurley warned that his cellphone battery was low; when she asked for his exact location, someone in the background yelled, “99 Nashua Street,” before the line went dead.

Minutes later, Mahoney arrived at that address — but Hurley was nowhere to be found. Six days later, his body was found in the Charles River, the cellphone from which he’d made that final call smashed nearby. Hurley’s death was eventually ruled an undetermined drowning, with the police stating that they found no evidence of foul play. Yet people who were close to Hurley — including Claire Mahoney — have disputed these claims, pointing to his damaged cellphone as well as injuries indicating blunt-force trauma, and a toxicology report that found high levels of GHB, commonly known as the date-rape drug.

But Hurley isn’t the first college-age male to have died under suspicious and hotly debated circumstances. More than a decade before Hurley disappeared in Boston, Fordham College senior Patrick McNeill vanished after stumbling out of a bar in 1997 on New York’s Upper East Side. McNeill was missing for more than a month before his body was found floating in the East River, and his death was later declared — like Hurley’s — to have been an undetermined drowning. But Kevin Gannon, one of the detectives who investigated McNeil’s case, didn’t agree with the official ruling on the 23-year-old’s death and promised the deceased’s parents that he would find them answers. More than 20 years later, he’s still trying.

In fact, Hurley and McNeil are part of what the now-retired Gannon, fellow former NYPD detective Anthony Duarte, and criminal-justice professor Lee Gilbertson have called an “epidemic” of college-educated young white men who have disappeared from nights out with friends and were later found dead in local rivers. Like Hurley’s death, most of these cases have been ruled accidental or undetermined drownings, with many blamed on alcohol consumption. But since 2008, Gannon, Duarte, and Gilbertson have argued that these deaths are instead the work of a ganglike organization of domestic terrorists — what has been coined the Smiley Face Killers because of happy-face graffiti found at purported crime scenes. According to the trio, these men didn’t drown but were instead targeted, kidnapped, and murdered by dangerous criminals who remain at large and continue to kill; the detectives believe the crimes are motivated by jealousy and reflect a coordinated effort to go after men that the killers perceive to be privileged, who Gannon characterized as “the best of the best.” It’s this ongoing threat, with more deaths that fit the profile occurring each year, that keeps the Smiley Face Murder Theory alive and led to Gannon, Duarte, and Gilbertson’s six-party Oxygen series Smiley Face Killers: The Hunt for Justice, which premiered in January.

Certainly, it’s a compelling idea — the type with the potential to rival that of Ed Kemper, the Co-Ed Killer, a necrophile who trolled California freeways looking for hitchhikers in the 1970s, or the still-unidentified Long Island Serial Killer, who dumped the bodies of sex workers on Gilgo Beach on the island’s South Shore. That is, if the Smiley Face Killers actually exist. And according to the FBI, the Center for Homicide Research, and many experts, that’s a big “if.”

When Gannon, Duarte, and Gilbertson publicly announced their theory about the Smiley Face Killers, in 2008, they claimed to have identified more than 40 potential murders that had been labeled accidental or undetermined drownings. Since then, they have developed additional physical evidence, and, perhaps most notably, expanded their database of potential victims of the Smiley Face Killers to 335 cases of suspicious drownings like that of Hurley. But as they outlined when we spoke for this piece, their evidence goes beyond circumstantial.

First and foremost, the trio point to the decomposition timelines. “The lack of decomposition on the bodies is inconsistent with the period of time that the victims are missing,” Gannon explains. Some of the cases examined in the Oxygen special include that of Dakota James, who was missing for 40 days but showed decomposition of only around three days, and Todd Geib, who had been missing for 21 days but showed decomposition of around 2.5 days. Gannon also noted that the presence of land insects, lividity patterns, and the lack of bloating associated with the recovered remains suggest that the victims died on land, not in the water. The detectives also pointed out the occurrence of a particular chemical. “We have the presence of GHB, which is a date-rape drug usually used to facilitate rape, in 99.9 percent of the cases,” Gannon notes. Though GHB isn’t typically included on post-mortem toxicology tests, many families of suspected Smiley Face victims have either requested that the coroner test for this chemical during the autopsy or sent Gannon, Gilbertson, and Duarte samples for them to test themselves. Taken together, the trio believe the forensic evidence proves that the victims were drugged before they were abducted, then murdered, and placed into the water.

While Gannon, Duarte, and Gilbertson’s primary goal is to have these deaths reclassified as homicides, a secondary priority is proving linkage between the cases. Besides the similarities in victim profile and circumstances around their disappearance and death, they also points to 13 symbols, including smiley-face graffiti, that they’ve located near what they believe to be the crime scenes.

As for why these deaths haven’t been labeled homicides, Duarte points to a “disconnect” between the police and the medical examiner’s office, noting that each division is often looking to the other for cues on how to proceed. “The medical examiner says, ‘We don’t know exactly how he died, so we need to wait for the police to let us know,’ ” Duarte says. “And the police say, ‘The medical examiner isn’t calling it a homicide, so we’re not going to make it a homicide.’ ” This type of coordination can pose challenges not only at the departmental level but also at the jurisdictional level, as cases where victims are found in rivers often require collaboration between state and local agencies. With more pressing investigations taking priority, the investigators feel that many of the cases were either overlooked or wrapped up too quickly. “Nobody’s looking beyond,” says Gannon.

But there may be other reasons that the police haven’t dug past accidental-drowning rulings to find evidence of the Smiley Face Killers. As much as Gannon, Duarte, and Gilbertson are convinced, there’s another possibility: that these deaths are nothing more than unfortunate accidents, and that the Smiley Face Killers hypothesis is nothing more than a conspiracy theory.

In April 2008, the day after the trio publicly announced their theory, the FBI released a statement that it had “not developed any evidence to support links between these tragic deaths or any evidence substantiating the theory that these deaths are the work of a serial killer or killers.” Instead, the letter says that “the vast majority of these instances appear to be alcohol-related drownings.”

Two years later, the nonprofit Center for Homicide Research in Minneapolis released a more comprehensive study titled “Drowning the Smiley Face Murder Theory.” In it, the center outlined 18 empirically driven points that “debunk” the idea that these deaths could be linked — let alone, at least in most cases, anything more than accidental drownings. This includes a lack of physical evidence of a serial killer, with researchers noting that the bodies were found without signs of torture, strangulation, or otherwise inexplicable blunt-force trauma, or other evidence that could point to “homicidal drowning,” itself an exceptionally rare crime. Instead, medical examiners almost universally ruled the deaths accidental or undetermined drownings. As for the presence of GHB, considered by some the smoking gun in Hurley’s case and others, detractors offer alternative explanations for these results, pointing to the chemical process of decomposition, the possibility that they took it willingly, and issues with the trio’s testing process.

The study also raises concerns about the smiley-face graffiti, as photographs of the graffiti show variation in style, size, and timing, including some that appear to have been painted long before the deaths occurred. Researchers point to a lack of consistency in terms of locating the graffiti; since authorities are only able to estimate where a body would have gone into the water, it is not possible to know exactly where the smiley-face graffiti should be located to fit the pattern. “Saying graffiti was found near the scenes is dubious at best,” says Canadian criminologist, author, and true-crime expert Michael Arntfield. “In most of these cases, we don’t know where the men went into the water or where they actually died.” Additionally, research conducted by Arntfield’s own students found that a smiley face was the most common non-gang graffiti tag in the U.S. national database. “You can find, in any city, a smiley-face graffiti tag somewhere along the water,” Arntfield says.

What do critics of the Smiley Face Murder Theory think is happening instead? Not a gang of killers, but a pattern of college-age white males at high risk for binge-drinking, risky behavior, and accidental drowning. According to a 2015 report by the Center for Disease Control, the two leading causes of death for white males under the age of 44 are accidents and suicide, respectively. A fact sheet by the CDC shows that men ages 18-34 are most likely to binge-drink, that binge-drinking is twice as common among men as it is among women, and that its risks include unintentional injuries. “The cases align with larger patterns we see datawise across the U.S., and not just in college towns,” Arntfield says. A report released in 2010 by police in La Crosse, Wisconsin — considered by some to be a hub of Smiley Face Killers — supported this explanation, noting that between the fall of 2006 and February 2010, police and foot patrol in La Crosse stopped at least 65 intoxicated persons from approaching local rivers late at night. The report went on to detail the cases of 20 near-drowning victims who had survived and whose testimonies pointed to dares, suicide attempts, and, most commonly, accidents. The Center for Homicide Research’s own team found that footwear slip marks are common on the riverbanks of Minneapolis.

Yet Gannon, Duarte, and Gilbertson aren’t convinced — or concerned — that their theory has been debunked. “They don’t even have a clue what we have,” Gilbertson says of what police handling individual cases know of the trio’s evidence related to GHB levels, lividity, insect presence, decomposition rates, and the presence of smiley-face graffiti. Though the detectives have presented their evidence in both the Oxygen series and a 2014 book titled Case Studies in Drowning Forensics, they don’t feel the majority of jurisdictions have taken their work seriously. Yet while the Smiley Face Murder Theory is largely dismissed by crime experts and law enforcement officials, some do give credence to Gannon, Duarte, and Gilbertson’s theory. “There are a lot of guys on the job, working in the field, boots-on-the-ground-type of guys, who agree with us,” Gannon says. “I have plenty of emails from officers and detectives who have told us that we’re on to something, and to keep going.” Some of these individuals, including Detective Sgt. William Fazekas, from Gary, Indiana, and Officer Joe Fisher, from Boston, as well as a number of forensic pathologists, appear in the Oxygen series.

And Gannon, Duarte, and Gilbertson aren’t the only ones who have kept the Smiley Face Murder Theory alive — in fact, the idea that there is a gang of dangerous killers targeting young white men has only gained momentum over the past decade. From armchair detectives to the loved ones of the deceased, proponents continue to take to TV specials, newspaper articles, and online forums to insist on what they are convinced is true: that these young men are victims not of youthful invincibility but of murder.

But for those who believe the deaths are, in fact, accidental drownings, this unwillingness to let go represents not the veracity of the Smiley Face Murder Theory but of the psychological factors that impact our relationship with true crime, ambiguity, and evil. Christine Sarteschi, an associate professor of social work and criminology at Chatham University, explains it as the human instinct to reject the unknown. “People don’t like to live with ambiguity,” she says. “They don’t like to not know.” Criminologist and serial-killer expert Scott Bonn also pointed to the fear of ambiguity as a driving factor for these cases. “We as people have a need for closure, a need to understand things,” Bonn says. Arntfield, who has studied the Smiley Face Murder Theory along with his students, calls this desire to assign a narrative an “intuitive human response to tragedy.” Identifying the threat also allows us to distance ourselves from its nuances. “The underlying human emotion is fear, and the need to control that,” Bonn says. “By reducing it to evil, we don’t have to understand it.” But this can also create a false sense of security: “It protects you. It reduces the world to us and them. And it enables you to point the finger, to have someone to blame.”

This desire to finger-point can also contribute to a larger phenomenon called moral panic, described as the spread of fear over an often-exaggerated or mischaracterized societal threat, from the Salem witch trials to the “satanic panic” of the 1980s. The spread of moral panics has grown with the expansion of media and its influence over society — when Jack the Ripper was supposedly stalking London, for example, it was in the early stages of tabloid newspapers. “As news spread around the world, people thought Jack the Ripper was in their backyard in Chicago,” Bonn says of the late-19th-century serial killer, who may have been multiple killers active at the same time. As Arntfield puts it, “Jack the Ripper and the Smiley Face Killer are two great examples of the press combined with opportunistic people turning a series of tragedies into a myth of a killer that doesn’t exist.”

But the reasons for attributing likely accidental deaths to something more nefarious can also be personal. “I don’t think people like the idea that their loved ones could have been blamed for something,” Sarteschi says. “They don’t like the idea that they could have done something differently and have lived.” It’s an especially prudent thing to consider within the context of the Smiley Face Killers, where many of the deaths occurred after the victim drank alcohol and/or stepped out alone. “The reality is, maybe, had that person not been drunk that night or gone out, then they may not have died,” Sarteschi notes, adding, “That’s a hard thing to sit with.”

Bryanna Fox, a former FBI special agent who teaches in the department of criminology and the department of mental health, law, and policy at the University of South Florida, added that the denial can often be a form of cognitive dissonance. “For many people, the idea that such a tragedy could occur to us, our sons, our brothers, or our friends is difficult, if not impossible, to truly digest and believe,” Fox says. “Therefore, the ability to mentally attribute these accidents to a ‘boogeyman’ who can be avoided, if known, alleviates the cognitive concern that such a terrible thing can happen to us or someone we know.”

While both sides continue to debate the Smiley Face Murder Theory, the families of men like William Hurley are stuck without closure. With law enforcement decision-makers satisfied with the official causes of death, Gannon, Duarte, and Gilbertson represent the only hope for those who insist the police have gotten the deaths of their loved ones wrong; in turn, the trio continue to cite the families as their inspiration and motivation.

Meanwhile, the bodies of young men continue to turn up in rivers across the northeast U.S. and beyond. And as long as they are classified as undetermined drownings, the Smiley Face Murder Theory will persist — and so will Gannon, Duarte, and Gilbertson.

In fact, the trio think they could be approaching a pivotal moment in the case. “When we put out who’s doing this and why, I don’t think [the FBI] will have any option but to get involved,” Gannon says. Nothing — not debunking attempts, FBI statements, nor expert analyses — will deter the trio from pursuing what they believe is the truth. “We have to do something to bring the individuals responsible for this to justice,” says Gannon. “And I’m telling you, we won’t stop until we do.”