Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Three Watertown police officers have recalled their chaotic gun battle with the Boston bombers four days after the explosions that killed three people and injured 264. Testifying at Dzhokhar Tsarnaev's trial on Monday, the officers also recounted the terrifying moment he raced towards them in his getaway car - but fatally struck his older brother, Tamerlan, as he fled. The brothers fired a gun at three police officers and hurled bombs at them, including one that was similar to the devices used in the April 15, 2013 attack, the officers testified. Watertown Police patrolman John Reynolds recalled chasing the brothers in two cars hours after they allegedly shot and killed a police officer in nearby Cambridge, and having a large bomb thrown at him and a colleague as they tried to arrest the Tsarnaevs.Three police officers testified about the harrowing gun battle in Watertown, Massachusetts during Tsarnaev's trial on MondayBefore their testimony, jurors visited the bullet-riddled vessel where he was found hiding after the shootoutThey were lifted inside the boat to see the notes he scrawled inside denouncing the U.S. for its wars in Muslim countriesTsarnaev, now 21, is on trial for the bombings that killed three and injured more than 260, but his attorneys say he was recruited by his brotherIf convicted, the same jury will decide if he should get the death penalty 
 Question:Tsarnaev, flanked by three attorneys and _ marshals, watched impassively from a table 50 feet away.
Output:
U.S.