-- Krystle Campbell, a 29-year-old freckle-faced woman described by her mother as having "a heart of gold."
-- Lingzi Lu, a Boston University graduate student in mathematics and statistics.
She and two friends were watching the race near the finish line when the blasts erupted, BU Today reported. The second student was in stable condition at Boston Medical Center; the third student was not hurt, it said.
The explosions wounded 183 people.
-- Martin's mother and sister are among the wounded. His mother underwent surgery for a brain injury, and his 6-year-old sister lost her leg.
-- Doctors say dozens of victims suffered injuries to their legs that involve blood vessels, bone and tissue.
-- The bombings resulted in at least 13 amputations and left doctors picking ball bearings out of victims in the emergency room, a terrorism expert briefed on the investigation said.
-- A lid to a pressure cooker, thought to have been used in the bombings, was found on a roof near the scene of the blasts, a federal law enforcement official with knowledge of the investigation tells CNN.
-- The two bombs hit 12 seconds apart near the marathon's finish line.
-- One of the two bombs was housed in a pressure cooker hidden inside a backpack, the FBI said. To maximize the impact of the shrapnel, the device may have included "nails, BBs and ball bearings."
-- The second bomb was also in a metal container, but there's not enough evidence to determine whether it too was in a pressure cooker, the agency said.
-- Evidence recovered from the scene will be sent to the FBI's lab in Quantico, Virginia, where analysts will attempt to reconstruct the devices used in the attack.
Pressure cooker bombs
-- The simplicity of the bomb makes it hard to trace it to any particular group, an official said.
-- The "recipe" for the bombs ignited by pressure cookers can be found widely on the Internet.
-- In 2004, Homeland Security issued an advisory about pressure cooker bombs.
-- They are made by placing TNT or other explosives in a pressure cooker and attaching a blasting cap at the top, the advisory said. Pressure cooker bombs are made with readily available materials.
-- Though it could indicate domestic terrorism, such bombs have been used in a handful of instances related to international terrorism attempts over the last few years, an official said.