Boston bombs 'triggered by remote control'

The Boston Marathon explosions which killed three people and injured more than 260 were triggered by a remote-controlled detonator, US officials said today.

They said the bombs were not very sophisticated. One described the detonator as “close-controlled” – meaning it had to be triggered within several blocks of the bombs.

It was not immediately clear what the detonation device was.

A criminal complaint outlining federal charges against the surviving bombing suspect, Dzhokhar Tsarnaev, described him as holding a mobile phone in his hand minutes before the first explosion.

Mobile phones have been used to trigger bombings in war zones.

Earlier, investigators recovered one handgun believed to have been used in a gun battle with police, two US officials said.

One official said the serial number on what they described as a 9mm pistol was scratched off.

Tamerlan Tsarnaev died in a shootout with police. His brother, Dzhokhar Tsarnaev, was later caught hiding in a boat.

Boston police commissioner Ed Davis says more than 250 rounds were fired in the shootout. Police said the men also used explosives.

Mr Davis said shots were fired from the boat where Dzhokhar Tsarnaev was found.

It was not clear whether he was armed when he was captured.