Boston police have released an audio recording of a 911 call made by a resident who saw a man covered in blood hiding in a boat on his drive – which turned out to be Boston bomber Dzhokhar Tsarnaev. Dzhokhar and brother Tamerlan had planted bombs at the marathon four days earlier, on 15 April 2013, killing three and leaving 270 wounded.

Tamerlan was killed in a shoot-out but Dzhokhar managed to flee despite being injured and took refuge in the covered boat in the Watertown district. The boat belonged to David Henneberry who noticed something unusual. Calling 911 he said: "I just looked in it and I found something on the outside and I got nervous. And I looked in and I saw blood all over the floor of the boat and there's a body in the boat."

The operator told Henneberry not to put himself at risk. "Stay where you are," he was advised. Henneberry then added: "He's in the boat laying the floor. Climb up the ladder you can open the hatch. He's in the boat."

Asked by the operator to confirm whether Tsarnaev is alive he said: "I don't know. The person didn't move when I opened up the door in the shrink wrap."

A Boston Police Department (BPD) helicopter then arrived overhead and was able to confirm Tsarnaev was still alive using infrared imaging. He was arrested and convicted of 30 charges relating to the attack and the murder of MIT police officer Sean Collier.

Speaking after his conviction Tsarnaev apologised for what he and his brother had done.

"I would like to now apologise to the victims, to the survivors," he told the court. "I want to ask forgiveness of Allah and his creation. I am sorry for the lives I have taken, for the suffering that I have caused you, for the damage I have done – irreparable damage. In case there is any doubt, I am guilty of this attack, along with my brother,"

After making the speech Tsarnaev was sentenced to death by legal injection. He is now the youngest person on death row in the US penal system, but is unlikely to be executed for at least a decade.