Boston bombing: Memorial held for officer Sean Collier

The memorial service at MIT
The memorial service at MIT Credit: REUTERS/Brian Snyder
The memorial service at MIT
The memorial service at MIT Credit: REUTERS/Brian Snyder
Members of the MIT community arrive for a memorial service for MIT police officer Sean Collier
Members of the MIT community arrive for a memorial service for MIT police officer Sean Collier Credit: REUTERS/Brian Snyder

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Boston bombs 'remote trigger'

US investigators have revealed the two bombs that went off at the Boston Marathon were detonated with the kind of remote control device used for a toy car.