Boston police and the FBI killed a man who had been under 24-hour surveillance by anti-terrorism forces on Tuesday, and now his motives are becoming clearer.

Usaama Abdullah Rahim, who lunged at cops with a military knife on the streets of Boston seconds before he died, had hopes to perform ISIS-style beheadings on police officers, as well as "Draw Muhammad" activist Pamela Geller, according to CBS News. David Wright, who authorities believe was planning these attacks with Rahim, was taken into custody on Tuesday in Massachusettes.

An FBI affidavit stated that Rahim told Wright, a relative of his, about a plan "to kill a person outside of Massachusetts." Wright responded by using the term "like thinking with your head on your chest," which CBS News say is "an apparent reference to beheadings carried out by ISIS."

The pair was set on harming Geller but changed direction towards the "boys in blue" because they would be easier to target, the court documents show.

"I can't wait that long," he said of the original beheading plan, CNN reported.

Last month, two men opened fire in North Garland, Texas (a suburb of Dallas) outside a contest for cartoon drawings of Prophet Muhammad that Geller planned. The gunmen were shot and killed by police.

Geller said that all Americans are in danger, not just her.

"I'm the number one target for ISIS right now," Geller told CBS News. "It won't end with me or the cops," Geller continued. "The one thing that's came out of Garland is ISIS is here. Islamic terrorism is here on the home soil on a weekly, sometimes a daily basis.

"They targeted me for violating Sharia blasphemy laws. They mean to kill everyone who doesn't do their bidding and abide by their law voluntarily. This is a showdown for American freedom. Will we stand against this savagery or bow down to them and silence ourselves?"

Authorities believe Rahim and Wright met with an unidentified third accomplice, who is still at large, in Rhode Island on Sunday.