Why are police searching & surveilling innocent citizens?

New York - On Nov. 17, Kira Moyer-Sims was near the Manhattan Bridge, buying coffee while three friends waited nearby in a car. More than a dozen blocks away, protesters gathered for an Occupy Wall Street “day of action,” which organizers had described as an attempt to block the streets around the New York Stock Exchange.       

Then, Ms. Moyer-Sims said, about 30 police officers surrounded her and the people in the car. All four were arrested, said Vik Pawar, a lawyer for Ms. Moyer-Sims and two of the others, and taken to a police facility in the East Village. He said officers strip-searched them and ignored their requests for a lawyer. The fourth person could not be reached for comment.

Ms. Moyer-Sims, 20, said members of the Police Department’s intelligence division asked about her personal history, her relationship with other protesters, the nature of Occupy Wall Street and plans for upcoming protests.
“I felt like I had been arrested for a thought crime,” she said.
Mr. Pawar said that the police had charged his three clients, Ms. Moyer-Sims, Angela Richino and Matthew Vrvilo, with obstructing governmental administration, but that the Manhattan district attorney’s office had declined to prosecute them.
Now they are preparing to sue the city, Mr. Pawar said, adding that the arrests had violated their constitutional rights.
“Not only are the police disrupting people’s rights to free expression,” Mr. Pawar said. “They are taking pre-emptive steps by arresting people who might be just thinking about exercising their rights.”  
 For the last few months, protest organizers say, NYPD police officers or detectives have been posted outside buildings where private meetings were taking place, have visited the homes of organizers and have questioned protesters arrested on minor charges.
“The NYPD surveillance does not appear to be limited to unlawful activity,” said Donna Lieberman, the executive director of the New York Civil Liberties Union. “We count on the police, of course, to be on the lookout for terrorists and terrorism, but to think you could be on that continuum just by going to a peaceful protest is nuts.”           http://www.nytimes.com/2012/03/12/nyregion/occupy-wall-street-protesters-complain-of-police-monitoring.html?_r=3