Additional information was released Wednesday about the killing of the campus police officer that touched off the nighttime gunfight and the daylong lockdown of the Boston area in search of the surviving suspect.
Investigators said they believe Sean Collier, 27, an MIT policeman, was ambushed while sitting in his cruiser on the Cambridge campus because the brothers wanted another gun. They said the pair fled without Collier's service revolver when they could not figure out how to release its triple-lock holster.
Collier's killing brought scores of officers into the area, and a motorist soon reported to police that his black Mercedes SUV had been carjacked by two men who said they were the marathon bombers and had killed a policeman.
Police were able to track the SUV from the driver's cellphone, which he left in the vehicle, setting off a police chase and high-drama events that eventually led to the death of Tamerlan Tsarnaev and the capture of Dzhokhar Tsarnaev.
Other developments in the bombing case:
-- Investigators said the two pressure cooker bombs that exploded near the marathon finish line were likely detonated by close-range remote controls like those used in kids toys.
-- Federal security officials in Washington were under fire for not sharing terrorist watch data on Tamerlan Tsarnaev in 2011 and 2012, when Russian authorities warned the FBI and CIA separately that he was a "strong believer" in radical Islam. House Speaker John Boehner said he wants to know "what agencies knew what, and the fact that it wasn't shared."
-- The mother of the Tsarnaev brothers told reporters in Russia that she will never accept that her sons planted bombs at the Boston Marathon. "America took my kids away from me," she said. She also said she regretted moving her family to the United States from the Dagestan region of Russia a decade ago. She and her husband later returned to Russia but the sons stayed in the Boston area. "Why did I ever go there? Why?" she said. "I thought America is going to, like, protect us, our kids. It's going to be safe."