DENVER —  City police monitored a group of teens known as the Trench Coat Mafia after the Columbine school massacre, intelligence files released this week show.

Investigators found no evidence of criminal activity, according to the files.

Officers opened a file on the teenagers -- who wore long trench coats and described themselves as outcasts -- six months after the April 20, 1999, shootings at Columbine High School.

Officers ran computer checks on about 75 teenagers who were either thought to be in the group or believed to be friends of those in the group, but found nothing.

Columbine killers Eric Harris and Dylan Klebold, who fatally shot 12 students and a teacher before killing themselves, had been rumored to belong to the Trench Coat Mafia. Investigators later concluded that they didn't.

The documents were among intelligence files that the city released as a result of an unrelated lawsuit in which the police are accused of violating the constitutional rights of protesters.

The American Civil Liberties Union sued the city last March after learning that the Denver Police Department had compiled surveillance files on at least 3,200 people and 208 groups. The organization said the police didn't just target known or suspected criminals, but also singled out peaceful activists.

The documents released Wednesday indicate that officers watched people ranging from anti-war protesters to members of militia groups and motorcycle gangs.