New York City police are investigating what they say is an online threat made against police officers by an apparent Occupy protester following a clash at Zuccotti Park

Police spokesman Paul Browne confirmed Sunday that the department was seeking a subpoena to identify the person.

The New York Post and Daily News report a message by an apparent Occupy protester saying they won't make a difference if they don't kill a cop or two was tweeted at about 11:40 p.m. Saturday.

Hundreds of protesters had returned to Zuccotti Park near Wall Street on Saturday to mark the six months that have passed since the movement began.

Authorities say 73 people were detained. It was unclear how many were still in custody Sunday afternoon.