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To catch criminals, police worldwide are using social networks, psychological tactics and TV programs.

Facebook scans private chatting sessions and posts to catch users who violate its terms of use or seek criminal activities, according to Reuters.

The world's largest social networking site immediately calls law-enforcement agencies after it finds and flags users who use its accounts for potential criminal activities, said Jeffrey Duncan, special agent supervisor for the Florida Department of Law Enforcement, in an interview with Reuters.

"A man in his early 30s was chatting about sex with a 13-year-old south Florida girl and planned to meet her after middle-school classes the next day," he said.

"Facebook's extensive but little-discussed technology for scanning postings and chats for criminal activity automatically flagged the conversation for employees, who read it and quickly called police. Officers took control of the teenager's computer and arrested the man the next day."

As long as information goes out on the Internet, "pressing the 'Delete' button cannot remove the information completely," Tang Lan, an expert on information security from the China Institutes of Contemporary International Relations, told China Daily.

Four out of five police officers said they use social media platforms to help them with their investigations, according to a survey recently published by LexisNexis Risk Solutions.

Social media is becoming a popular tool in law enforcement, especially in departments serving smaller cities, the survey said.

Meanwhile, UK police also set traps for suspects using attractive windfalls as bait.

In one case, undercover Derbyshire police officers sent letters to dozens of people who had evaded arrest asking them to call a marketing company to collect a free crate of beer, a report in The Telegraph said.

The fugitives were told that they needed to arrange a date and time for the free alcohol to be dropped off at a certain address.

But instead of getting free beer, the wanted men found themselves confronted by police, handcuffed and under arrest.

A total 19 suspects fell for the hoax and called the number on the letter, which put them through to police officers.

Chief Inspector GrahamMcLaughlin, who is leading the project known as Operation Rocky, told The Telegraph:

"It has been very cost-effective as it can take a lot of time and money to track people down. We will continue to use new tactics when necessary."

Besides challenging psychological capability of the fugitives, police in the UK, the US, Germany and many other countries also use TV shows, which reconstruct the crime scenes, to find criminals.

In 1984, BBC began to broadcast the TV program Crimewatch, which reconstructs major unsolved crimes with the purpose of gaining information from the public.

According to producers of Crimewatch, about a third of its cases are solved, half of those as a direct result of viewers' calls.

Thanks to the program, some of UK's most notorious criminals were caught. Among them were Michael Sams, a rapist, kidnapper, extortionist and murderer.

.A similar program, America's Most Wanted, was introduced in the US in 1988. It is hosted by former Hollywood real estate businessman John Walsh, who created the show after the murder of his 6-year-old son in 1981.

（中国日报网英语点津 Helen 编辑）

About the broadcaster:

CJ Henderson is a foreign expert for China Daily's online culture department. CJ is a graduate of the University of Sydney where she completed a Bachelors degree in Media and Communications, Government and International Relations, and American Studies. CJ has four years of experience working across media platforms, including work for 21st Century Newspapers in Beijing, and a variety of media in Australia and the US.