New York City police were investigating Sunday an "Occupy Wall Street" protester who made threats on Twitter about killing police as hundreds clashed the previous day with cops at Zuccotti Park.

"We won't make a difference if we don't kill a cop or 2," Twitter user "Smackema1" posted about 11:40 p.m. with a link to Ustream, which was showing footage of the protests at the Lower Manhattan park where "Occupy Wall Street" began last September, the New York Post reported.

The author also posted several other comments Saturday about the protests, the New York Daily News reported, and police are now seeking a subpoena to help them discover who was behind the tweet, NYPD spokesman Paul Browne said.

An anonymous man claiming to be behind the tweets later defended them to the Daily News, saying, "It's not like I meant anything of it. Who takes anything like that seriously? I'm in Florida, what am I going to do?"

He said he had never attended an "Occupy Wall Street" protest, but had followed them online.

Police also said Sunday they were separately investigating threats made to two cops and their families.

There were 73 people arrested Saturday when protesters returned to Zuccotti Park to mark six months since the "Occupy Wall Street" movement's inception.

Fourteen of the arrests were made before officers raided the gathering, police sources told FOX News Channel.

The protesters erected a tent in Zuccotti Park -- reminiscent of the around-the-clock encampment that began at the site on Sept. 17, 2011 and remained for nearly three months, inspiring similar efforts across the US and around the world. Others held pop-up tents over their heads, according to the Post.

The large-scale clashes began when law enforcement presence increased dramatically after 11:00pm local time.

"There was a change in mood," 32-year-old student Shane Patrick told The Wall Street Journal. "They made an announcement that we had to get out. Once they pushed people out, they immediately started snaking the barricades and locking the park down."

Some protesters said police used physical force to drive demonstrators from the park.

"They were beating us and hitting us," 38-year-old Felix Rivera-Pitre said. "They came at us with batons and started pushing everyone out of the park."

One person threw a glass Snapple bottle towards officers, according to the Post.

Several protesters said a young woman had a seizure as she was being escorted to a van by police. An ambulance arrived at the scene about 20 minutes later, one protester said.