BOSTON — The twin killer bombs that exploded seconds apart at the Boston Marathon contained metal pellets, including nails and ball bearings, packed into 6-liter pressure cookers with timers, investigators reported Tuesday.
They said the bombs were hidden inside black duffel bags dropped alongside spectator-crowded Boyleston Street near the 26.2-mile course’s finish line. They said a circuit board recovered at the scene may have been used to remotely detonate the bombs.
The Monday afternoon bomb blasts killed three spectators: Martin Richard, 8, who attended the race with his family, Krystle Campbell, 29, who was waiting to take a picture of her best friend’s boyfriend crossing the finish line, and a Boston University graduate student. The third victim’s name was withheld, pending notification of family.
Officials said 176 runners and onlookers were injured, 17 critically. A massive police investigation was under way for clues to the who and why of the tragedy.
“This was a heinous and cowardly act,” President Obama said Tuesday. “And given what we now know about what took place, the FBI is investigating it as an act of terrorism.”
Investigators said the first bomb exploded across from the finish line viewing stands where Massachusetts Gov. Deval Patrick and other dignitaries had been sitting when the first runners finished two hours before. The second bomb was set off about 100 yards down the street outside the Forum restaurant.
Authorities did not know who planted the bombs. The FBI, which is heading the investigation, said there were no suspects at present.
Investigators were studying surveillance video from security cameras stationed along the marathon course, including the finish line. They also viewed television footage of the race and numerous smartphone video and photos submitted by spectators.
Richard DesLauriers, special FBI agent in charge of the investigation, said “voluminous tips” had been provided to law enforcement officials.
The twin explosions occurred more than four hours after the start of the 117th Boston Marathon and after more than half of the 23,000 runners had completed the race.
Officers sweeping the area screened other suspicious packages in the vicinity, but officials said they did not discover any other explosives. They also said the finish line area had been checked for suspicious objects an hour before the bombs exploded.
Six Boston hospitals treated the injured, several of whom were in critical condition. A doctor at Massachusetts General Hospital, where 30 of the victims were taken, said most of the serious wounds involved burns and lower body extremities.
Dr. George Velmahos, chief of trauma surgery at Mass General, said some patients withstood 40 or more metal pellets, nail-like fragments and other sharp objects that were likely packed into the bombs.
Investigators said they did not know if the bombings were connected in any way to the fact the marathon is always staged on Patriots Day. It was also noted that Monday was the deadline for filing federal tax returns.