NEW YORK (AP) — New York Police Department documents show that undercover officers attended meetings of liberal political groups and kept intelligence files on activists.The records show how, since the attacks of Sept. 11, 2001, counterterrorism tactics have been used to monitor even lawful activities.In April 2008, an undercover officer attended the People's Summit in New Orleans, a gathering of liberal groups opposed to U.S. economic policies. Documents obtained by The Associated Press show police noted groups and activists in attendance. No crimes were alleged.The infiltration echoes tactics used before New York's 2004 Republican National Convention. Police said they had to keep tabs on groups that might get violent, as they have in other cities.Police say they can go wherever the public can go to look for signs of crimes.