Thousands of police officers from across the US gathered at a memorial for the university police officer allegedly killed by the Boston bombing suspects on Wednesday, as information continued to emerge on the blasts that killed three and wounded 262 people.
US vice-president Joe Biden spoke at the service, describing the Tsarnaev brothers, who the FBI believe planted two explosive devices at the Boston Marathon finishing line, as "two twisted, perverted, cowardly, knockoff jihadis".
Tamerlan Tsarnaev, 26, died in a botched escape attempt after a shootout with police officers late on Thursday night. Dzhokhar Tsarnaev, 19, was captured on Friday and is in hospital, where he is said to be in a stable condition. He has been charged with using and conspiring to use a weapon of mass destruction, a count that carries a possible death penalty.
Speaking at a service for Sean Collier, the 26-year-old Massachusetts Institute of Technology officer who died after allegedly being shot by the bombing suspects, Biden said the bombing had been conducted to "instil fear", but would not succeed. Addressing Collier's family, Biden said: "My heart goes out to you." He added: "I hope you find some solace in this time of extreme grief."
Biden invoked the loss of his own daughter, who died along with his wife in a car crash in 1972, as he addressed Collier's parents directly. "The moment will come when the memory of Sean is triggered and you know it's going to be OK," he said. "When the first instinct is to get a smile on your lips before you get tear to your eye."
As the service took place it emerged that a US team of investigators had travelled to the Russian province of Dagestan on Tuesday to question the Tsarnaev parents, Anzor Tsarnaev and Zubeidat Tsarnaeva. Officials are investigating Tamerlan Tsarnaev's trip to Russia in 2012 and whether he met with extremists during that time.
Anzor Tsarnaev and Zubeidat Tsarnaeva told a Russian news agency that they will fly to the United States on Thursday.
In the US, more details emerged about the bombs allegedly constructed and detonated by the Tsarnaev brothers. Officials say the two devices which exploded by the finishing line of the marathon were triggered by a remote-controlled detonator, the AP reported on Wednesday. Officials do not believe the bombs were sophisticated, it said, quoting one investigator as saying the detonator was "close-controlled" – meaning it had to be triggered within several blocks of the bombs.
It is not known how the bombs were detonated. A criminal complaint outlining federal charges against the surviving bombing suspect, Dzhokhar Tsarnaev, described him as holding a cellphone in his hand in the minutes before the first explosion.
Investigators in the US have recovered only one handgun believed to have been used by the Tsarnaevs in a shootout with police, according to the AP. It cited two officials as saying a 9mm pistol had been recovered but no other weapons had been found. The serial number had been scratched from the gun, the AP reported.
Tamerlan Tsarnaev was killed following a shootout with police. Authorities said he had run out of ammunition when he was struck by a car driven by his younger brother and dragged some distance.
Police in Rhode Island said they were working on Wednesday to determine whether a body found in Providence Harbor is that of a Brown student, missing since March, who was mistakenly linked to the Boston bombings last week.
Sunil Tripathi went missing on 16 March and was wrongly implicated in the marathon bombings by Reddit users who erroneously claimed he was the suspect wearing a white hat. That man turned out to be Dzhokhar Tsarnaev.