"When we meet with the police and we talk about investigative techniques, when they are on these social media sites, we'll give them certain directions," Ed Carroll, head of the Gang Bureau of the Brooklyn district attorney's office, said Tuesday. "We don't want to set up any situation where anyone is being entrapped or put in a position where they're going to agree to commit a crime."
Police officials from San Diego and Atlanta who attended the California gathering on Tuesday said their departments also monitor Facebook and other social media to learn what gang members are saying about shootings and other crimes.
"It's no different than interviewing a witness or knocking door to door, doing canvasses," said Carlos Campos, spokesman for the Atlanta Police Department. "Technology has just given us another angle for investigating."
In Chicago, police also built a database of the city's gang members and provide commanders with software that allows them to send officers to spots where they expect a gang to retaliate for a shooting.
A federal judge in New York has already weighed in on the privacy issue, siding with prosecutors in a gang case in the Bronx.
In that case, federal investigators infiltrated the private Facebook posts of a suspected leader of a drug crew leader by using the account of a "friend" who became an informant. Court papers says the posts included comments about cocaine deals such as, "I'm trying to see the man for like 600 grams," and photos of the suspect making gang hand gestures.
Defense attorneys tried to have the material thrown out, arguing it was obtained in violation of the Fourth Amendment protection against unreasonable search and seizure.
In a decision last month, U.S. District Judge William H. Pauley wrote that defendant Melvin Colon's "legitimate expectation of privacy ended when he disseminated posts to his 'friends' because those 'friends' were free to use the information however they wanted — including sharing it with the government."
Associated Press writers Verena Dobnik in New York and Don Babwin in Chicago contributed to this report.