Investigators search for sender of package bombs to Trump critics

WASHINGTON - Investigators have been searching across the United States for the culprit and motives behind the bizarre mail-bomb plot aimed at critics of the president, analyzing the crude devices to reveal whether they were intended to detonate or simply sow fear less than two weeks before midterm elections in the US.

Three more devices were linked to the plot on Thursday - two addressed to former vice-president Joe Biden and one to actor Robert De Niro - bringing the total to 10 in an outbreak of politically loaded menace with little if any precedent. Authorities warned there might well be more.

Law enforcement officials said the devices, which contained timers and batteries, were not rigged like booby-trapped package bombs that would explode upon opening. But they remained uncertain whether the devices were poorly designed or never intended to cause physical harm.