It's at this time, Tazhayakov later recalled, that Kadyrbayev texts Phillipos so they can all meet at Dzhokhar Tsarnaev's dorm room.
Dzhokhar Tsarnaev's roommate lets all three young men into the room, telling them that Tsarnaev had left a few hours earlier. Just before they go in, Tazhayakov says that Kadyrbayev showed them a text message from Tsarnaev saying, "I'm about to leave if you need something in my room take it."
"When Tazhayakov learned of the message, he believed he would never see Tsarnaev alive again," a federal affidavit states.
While watching a movie, the three -- Kadyrbayev, Tazhayakov and Phillipos -- spot a backpack with fireworks that have been opened and emptied of powder. Phillipos tells investigators that he noticed about seven tubular fireworks, each between six to eight inches long, in the backpack.
According to Tazhayakov's account in an FBI affidavit, Kadyrbayev also finds a jar of Vaseline that he thought Dzhokhar Tsarnaev used "to make bombs."
The same affidavit states that, at that time, Kadyrbayev knew Dzhokhar Tsarnaev was involved in the Marathon bombing -- an assertion that his lawyer denies.
The young men take take the backpack out of the dorm room, as well as Tsarnaev's laptop.
Around 10 p.m.: Kadyrbayev, Tazhayakov and Phillipos take the backpack and computer to the New Bedford, Massachusetts, apartment shared by the first two young men. There, they watch news reports that broadcast photos of the man who would later be identified as their mutual friend, Dzhokhar Tsarnaev.
Phillipos says later that Kadyrbayev and Tazhayakov both "started to freak out, because it became clear from a CNN report that we were watching that (Dzhokhar Tsarnaev) was one of the Boston Marathon bombers." He adds he did not understand much of what the roommates, Kadyrbayev and Tazhayakov, said afterward because they talked mostly in Russian.
According to Kadyrbayev, the three collectively decide to throw away the backpack and fireworks because they don't want Dzhokhar Tsarnaev to get in trouble. Kadyrbayev puts them in a black trash bag, which he tosses in a dumpster outside his apartment.
In federal documents, Tazhayakov gives different timing, as to when the backpack was discarded. He said it happened around 6 a.m. the next day, after he, Kadyrbayev and Phillipos see news reports that identify their friend, Dzhokhar Tsarnaev, as one of two Boston attack suspects. He said that Kadyrbayev decided -- and Tazhayakov agreed -- that they should toss the backpack.
Phillipos said Kadyrbayev asked him about 11 p.m., and he responded, "Do what you have to do." By the time he woke up after a two-hour nap, Phillipos recalled, the backpack was gone. After waking, Phillipos stays up until 4 a.m. Friday watching television with Tazhayakov.
11 p.m. Massachusetts Institute of Technology police officer Sean Collier, 26, is shot dead on the school's Cambridge, Massachusetts, campus -- a killing authorities later link to the Tsarnaevs.
Friday, April 19
Early hours: Police say the two suspects hijack a car at gunpoint in Cambridge, Massachusetts, taking the driver as a hostage. One suspect tells the driver they are the Boston Marathon bombers, and the suspects talk openly about heading to New York.
Eventually, though, the driver is able to escape his captors by running from them into a gas station convenience store.
Thanks in large part to information from the hostage, authorities track down the suspects. A chase ensues, during which the suspects toss explosives and exchange gunfire with police.
Tamerlan Tsarnaev dies after the gunfight, while his brother eludes authorities.
Daytime: Boston and surrounding communities are put on lockdown -- with schools closed, public transit halted and people ordered off the streets -- as authorities hunt for the surviving suspect.
Sometime that afternoon, some 60 miles south in New Bedford, a garbage truck clears the dumpster outside Kadyrbayev and Tazhayakov's apartment. The dumpster had contained Tsarnaev's tossed backpack.
6 p.m. to 9 p.m.: After the lockdown is lifted, a resident goes outside to check on his boat parked in the backyard and notices blood inside. His tip leads to a large-scale law enforcement effort that culminates with the capture of Dzhokhar Tsarnaev.
When the suspect is found, he has visible injuries including apparent gunshot wounds to his head, neck and legs and hand. His wounds are treated, and he is transported by ambulance to Boston's Beth Israel Deaconness Medical Center.
April 19 and 20
Investigators interview Dias Kadyrbayev over parts of two days. He discusses his relationship with Dzhokar Tsarnaev, whom he met when they both enrolled at the University of Massachusetts-Dartmouth in fall 2011. They hung out in and outside school, with Kadyrbayev noting that he'd repeatedly visited Tsarnaev's home in Cambridge and met his family members.
FBI agents questioned Kadyrbayev and Tazhayakov for about 10 hours on April 19, then they were taken into custody the next day, said Robert Stahl, Kadyrbayev's lawyer. They remained detained for several days on alleged visa violations.