The hours since the FBI released images of the two men suspected in this week's Boston Marathon bombings have been rife with new developments in the case. Among them:
-- Late Thursday, police respond to a call on the campus of the Massachusetts Institute of Technology, where university police officer Sean Collier, 26, was shot. He died from his injuries. Police believe the bombing suspects were responsible for the shooting.
-- Police say the two suspects hijack a car at gunpoint in Cambridge, Massachusetts, taking the driver as a hostage. The suspects tell the driver they are the Boston marathon bombers, a law enforcement source said
-- The hostage is released at a gas station a short time later.
-- The two suspects pull over to transfer materials into their new car, then throw one grenade and five pipe bombs at police chasing them, one FBI and one Department of Homeland Security official told CNN. Three of those explosives detonated, two did not, the officials said.
-- Police, who were tracking the vehicle using its built-in GPS system, pick up the chase in Watertown. The pursuit goes into a residential neighborhood, with the suspects throwing explosives and firing shots at officers, police say.
Officers fire back, striking a man later identified as 26-year-old Tamerlan Tsarnaev. The man -- who was suspect No. 1 in the images released late Thursday afternoon by the FBI -- was wearing explosives and an explosive trigger when his body was recovered, a source briefed on the investigation tells CNN.
-- Authorities later announce that they recovered a pressure-cooker bomb after the pursuit into Watertown, a source briefed on the ongoing investigation said. They also recovered a significant amount of homemade explosives in Watertown, Massachusetts State Police spokesman David Procopio said.
-- The suspects are identified as Tamerlan Tsarnaev and his 19-year-old brother Dzhokar.
-- The brothers came from the Russian Caucasus region and moved to Kazakhstan at a young age before coming to the United States several years ago. Dzhokar Tsarnaev was 8 years old at the time, their mother Zubeidat Tsarnaeva tells state-run Russia Today from Dagestan.
-- A federal official tells CNN that Dzhokar Tsarnaev came to the United States as a tourist with his family in the early 2000s and later asked for asylum. He became a naturalized U.S. citizen in 2012.
-- Dzhokar, a University of Massachusetts-Dartmouth student, was one of 45 high school seniors awarded a $2,500 scholarship by the Massachusetts city of Cambridge.
-- Tamerlan Tsarnaev was not a naturalized citizen, said an official, who spoke on condition of anonymity. He came "a few years later" and was lawfully in the United States as a green-card holder.
-- Tamerlan Tsarnaev studied engineering at Bunker Hill Community College just outside Boston, but had taken the year off to train as a boxer, sources told CNN.
-- In 2009, Tamerlan competed in a Golden Gloves match -- heavyweight division -- in Salt Lake City, losing in the first round.
-- Dzhokar Tsarnaev's friends express shock about his suspected involvement in the bombings. His Cambridge Rindge and Latin high school classmate Eric Mercado tells CNN "there were no telltale signs of any kind of malicious behavior."
-- Larry Aaronson, Dzhokar Tsarnaev's neighbor and a former teacher at the high school Tsarnaev attended, describes him as "caring," "jovial" and "so grateful to be here."
-- The mother of the Tsarnaev brothers refuses to believe they were involved in the marathon bombings and subsequent shootout. "It's impossible for them to do such things. I am really telling you that this is a setup," she says.
-- Their father, Anzor Tsarnaev, speaking to Russian state-run Zvezda TV, accuses someone of framing his sons. "I don't know who exactly did it. But someone did," he says.
Boston area locked down:
-- Around 2 a.m., police begin ordering Watertown residents to turn off their cell phones.
-- At least 12 universities and colleges, along with Boston Public Schools and Cambridge Public Schools, announce Friday morning that they will be closed for the day because of police activity.
-- Authorities later Friday ask that people in Watertown, Boston and Cambridge, where the two suspects lived, not leave their homes, as authorities try to hunt down the remaining suspect.