makeshift memorial for Boston Marathon attack
makeshift memorial for Boston Marathon attack Reuters

The brothers suspected of carrying out the deadly attacks on the Boston Marathon planned to head to Manhattan to party after the explosions, New York City's police chief said.

Either Dzhokhar or Tamerlan Tsarnaev apparently said "Manhattan" in a conversation overheard by the driver of the sports utility vehicle they carjacked in Cambridge, Massachusetts, last week before a showdown with police, Ray Kelly said, according to the AFP news agency. 

"They were speaking in either Chechen or Russian, a language the driver didn't understand. But he thought he heard the word 'Manhattan' in their conversation," Kelly told reporters.

"The information that we received said something about partying or having a party. The bit of information we have, they may have been words to the effect of coming to party in New York."

According to The Boston Globe, the vehicle's owner told police that Tamerlan threatened him, saying, "We just killed a cop. We blew up the marathon. And now we're going to New York. Don't f... with us," according to AFP. 

Shortly after hearing the conversation, the driver was able to free himself from the siblings, who were later tracked down by police. The chase triggered a shootout in which Tamerlan, 26, was killed. Dzhokhar, 19, was captured late Friday after a massive manhunt.

The younger Tsarnaev has been charged with federal terror offenses including the use of a weapon of mass destruction in the twin blasts on April 15 that killed three and wounded 264 people at the Boston Marathon's finish line.

If convicted, the teen, who is hospitalized in fair condition, could face the death penalty.

At a memorial for a Massachusetts Institute of Technology, US Vice President Joe Biden called the two suspects "twisted, perverted, cowardly, knock-off jihadists."

"We have suffered. We are grieving. But we are not bending. We will not yield to fear. We will not hunker down. We will not be intimidated," Biden said in his eulogy for a police officer who was allegedly slain by the brothers after the bombings.

Meanwhile, officials said the CIA asked the top US counterterrorism agency to add Tamerlan's name to a terror watchlist more than a year before the attacks.

The spy agency made the move after Russian officials contacted their CIA counterparts in September 2011 about concerns they had over possible terror ties of the now deceased suspect.