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At a digital-forensics conference in 2011, British police asked Tim Grant if he could help undercover agents pose as young girls online. Grant, the director of Aston University’s Center for Forensic Linguistics, had just given a talk on how to identify the author of online messages by parsing their language. An officer in a regional organized-crime unit came up to him, he says, and told him there was a case the police wanted help with.

According to Grant, the officer explained that adult agents would take on the roles to lure out people who use the internet to abuse children. These undercover agents would step in for young people who were already being pursued online by “finding out about a child’s school, the uniform they wear there, their likes and interests, all by reading the previous chat,” Grant says. “But [the officer] felt there was something missing: getting the language right.”

The officer hoped that Grant could teach the police how to talk like kids. “That was the start of it,” Grant says.

Seven years later, it’s a regular part of Grant’s job to help send police officers into dark corners of the internet. In his day job at Aston University, he analyzes the strategies criminals use to goad children into sharing explicit images of themselves or meeting in person, and publishes academic papers on his findings. But he’s on the U.K. National Crime Agency’s list of expert advisers, and around 10 times a year a police force will bring him onto a case. “It can be helping with infiltration strategies on the dark web, or assisting them by deanonymizing offenders,” Grant explains.

He and a colleague also helped establish a three-month distance-learning course for officers, part of which trains them to assume the identity of a 14-year-old girl being “groomed” online—the process by which perpetrators steer ostensibly casual interactions toward sexual exchanges or encounters. On top of that, Grant’s work helps inform officers who take on the roles of the image and video traders themselves, trying to sneakily gather intelligence on whom police can ensnare next.

Those who want to abuse children have long been locked in a technological arms race with law enforcement, with tactics including hidden IP addresses, offshore servers that host illegal forums, and the meticulous social-engineering trickery. “What these people have done is developed very sophisticated ways of hiding themselves,” says David Shemmings of the Center for Child Protection at the University of Kent. “I don’t know whether they are actually one step ahead of the security services, but they certainly believe they are.”

Grant is the trick up law enforcement’s sleeve to make sure officers keep up.


Studies carried out in the U.S. and Europe over several decades indicate that up to one in eight girls and one in 10 boys have suffered sexual abuse. The numbers appear to be rising: In 2004 to 2005, there were 1.7 child sexual offences reported per 1,000 children in the United Kingdom, including instances of both physical abuse and indecent photos; by 2015 to 2016, that had risen to 4.9 per 1,000. The number of defendants who were prosecuted for offences involving images of children in the U.K. rose from just over 1,000 in the year 2000 to 3,500 in 2016.

This trend can be attributed to growing awareness of child exploitation and willingness to speak up about abuse in recent years. But that like doesn’t explain all of it. “The reason we’ve seen an increase is perverts and abusers have recognized what a relatively easy way it is to inveigle their way into the lives of our children” by using the internet, says Peter Saunders of the U.K.’s National Association for People Abused in Childhood.

In response, vigilante groups of “pedophile hunters” have sprung up across the world. The American organization Perverted Justice has worked with NBC on To Catch A Predator. In the U.K., some of the fly-by-night groups include Dark Justice. Whether these groups help or hinder the policing of child sexual offences is hotly debated, but their unofficial work does have an impact: Evidence collected from vigilante groups was used to charge 150 suspected offenders in England and Wales in 2017, up sevenfold since 2015.

Still, the scattered groups across the globe taking justice into their own hands aren’t the frontline of the official forces battling against the rising tide of child sexual abuse and exploitation. In the U.K., at least, that’s the police. And the police know what they know in large part thanks to Tim Grant.

In one 2017 paper, co-written with his colleague Emily Chiang, Grant identifies 14 “rhetorical moves used in chatroom grooming” and unpacks “the broad structures that grooming conversations take,” based on transcripts of real child grooming collated by Perverted Justice. The most common approach groomers take, he finds, is that they build a connection before introducing any sort of sexual component. And they try hard to keep the conversation going, sexual or not. One of the biggest tells is what Grant calls the “mitigating lol”—a way of downplaying a serious sexual request, such as “u should make a nude vid and send it to me,” by adding the word “lol” at the end. “[Its] use here implies something vaguely playful or unserious about these contributions,” Grant and Chiang write. Most offenders introduce sexual overtones early in a conversation, they find.

To teach police officers how to play into these conversations, Grant’s course on becoming a 14-year-old girl throws its students in at the deep end. The officers are given a four-hour crash course in vocabulary, spelling, and conversation, then given two hours to digest 30 pages of chat logs from prior anonymized cases before they try out adopting the persona of the girl. Officers are encouraged to note down rules on spelling abbreviations, common misspellings, and sentence lengths.


Such fine-grain analysis of the methods and modes of perpetrators wasn’t how Grant began his work. “I did it based on my instincts for a while, then got a government research grant to do it properly,” he explains. A two-year research project showed what linguistic features child sexual abusers use and what words are most likely to give away the identity of undercover offices, and validated the training he gave police officers for six years before his course was taken over by the U.K.’s College of Policing. Many of the techniques Grant honed through his research are still used—while his research and his individual projects with police forces hasn’t stopped.

Grant is a professor and Director of the Centre for Forensic Linguistics at Aston University. (Courtesy of Tim Grant)

The U.K. National Crime Agency did not respond to a request for comment on Grant’s involvement in undercover investigations, and Grant himself refrained from divulging every element of his work to me, on the grounds that certain details could help tech-savvy offenders sniff out undercover officers. But what he shared indicates how totally he encourages police to subsume themselves in the identity of either a vulnerable child or a participant in forums promoting abuse. Any unobservant reader could identify the features of someone’s writing that makes it uniquely their own, Grant says. It might be an overreliance on a particular word, the placement of “like” in sentences, or a preponderance of semi-colons. “Without training, those will be overused by the person assuming the identity,” he says. “As well as becoming the other person, you have to not be yourself.”

Every step is designed not to draw attention to infiltrating officers. In the case of forums promoting abuse, “you want them to fit in,” Grant says. Aware of scrutiny from law enforcement, members of illicit groups are often hyper-attentive to any newcomers and their foibles—and are highly skeptical of those who don’t follow community norms. “What we’ll do in those situations is help the police examine the social rules of the forum and understand if you want to be someone in the background but still participating, what language style should you adopt?”

Undercover investigations are a contentious topic in the U.K. and elsewhere. Debates have long raged over how far agents should be allowed to go with false identities, and in what contexts. In 2011, a number of British spies were accused of developing intimate relationships with members of U.K. activist groups they were investigating, including agents who allegedly lived with their partners for several years, had children, then disappeared once their assignments were done. A broader public inquiry into years of alleged undercover infiltration of British political groups is ongoing. In the context of such extreme cases, Grant’s mandate to officers to become someone else can take on an uncomfortable tenor.

But Grant remains committed to the value of his work. “It’s exhausting and draining,” he says. “Those moments you feel you’ve made a substantial contribution towards catching a bad guy don’t come along often, but at those moments the rewards are enormous.”

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