Federal authorities say the person or persons responsible for yesterday's attack on the Boston Marathon likely used ordinary pressure cookers packed with shrapnel such as nails, metal shards or ball bearings. And the devices were left on the ground in bags or backpacks made of nylon.

That information was shared in hopes it will trigger leads that put investigators on the trail of the person or persons responsible. Pressure-cooker explosives have been used in international terrorism, and have been recommended for lone-wolf operatives by Al-Qaida's branch in Yemen.

But officials say information on how to make the bombs is readily found online, and that there is no rush to link the attack to overseas terrorists. Congressman Peter King, a member of the House intelligence committee, says the attack could have been carried out by someone from overseas or "a homegrown white supremacist" who fashioned the devices on information found on the Internet.

The bombs exploded 10 or more seconds apart, tearing off victims' limbs and spattering streets with blood. The blasts killed an 8-year-old boy, a 29-year-old woman and a third person identified only as a Boston University graduate student.

Scores are being treated for injuries, some of them severe.