The 2013 detonation killed three people and injured over 270
The dramatic phonecall which led to the capture of Boston Marathon bomber Dzhokhar Tsarnaev has been released by police.
Watertown resident David Henneberry checked the boat in his garden and found it covered in blood - and saw someone inside.
He called 911 and 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."
Tsarnaev and his brother Tamerlan detonated two home-made bombs at the finishing line of the Boston Marathon on 15 April 2013.
It killed three people and injured more than 270 others.
The pair went on the run, and a shootout in the early hours of 19 April left Tamerland dead and Tsarnaev critically injured.
He eventually hid in Mr Henneberry's boat, where he was discovered.
The operator told Mr Henneberry to "stay where you are", before Mr Henneberry added: "He's in the boat laying the floor.
"Climb up the ladder you can open the hatch. He's in the boat."
The operator asks: "Is he alive?" to which Mr Henneberry replies: "I don't know.
"The person didn't move when I opened up the door in the shrink wrap."
Mr Henneberry was told repeatedly to stay safe, but at one point the caller said: "I'm outside," to which the operator said urgently: "Go back inside. Don't put yourself in harms way. Don't go near the boat."
A police helicopter was scrambled and infra-red cameras showed he was still alive.
As the rapid response team arrived, Mr Henneberry told the operator: "They're all here. I'm going to hang up."
Following a stand-off, Tsarnaev was arrested and later sentenced to death by lethal injection.