U.S. President Barack Obama makes a statement on the Boston bombing from the White House in Washington April 16, 2013. Two bombs ripped through the crowd at the finish line of the Boston Marathon on Monday, killing three people, maiming others and injuring more than 100 in what a White House official said would be treated as an "act of terror."
BOSTON — President Barack Obama called the Boston Marathon bombings an "act of terror" on Tuesday and investigators said no additional explosive devices have been found other than two that detonated near the finish line, a development that could complicate the case.
Law enforcement officials, who asked the public to turn over any photos or video of Monday's marathon and the blasts, did not disclose any possible leads in the investigation. No one has been arrested, police said.
Late on Monday, police searched a Boston area apartment of a Saudi Arabian student who was injured in the blast, law enforcement sources said. But they said evidence showed that the student was expected to be cleared of suspicion and that he was unlikely to shed any light on the attack.
Numerous other theories and leads in the investigation are being looked at, according to the same sources, who asked not to be identified.
Current and former counter-terrorism officials said that the Boston bombs were built using pressure cookers as the superstructure, black powder or gunpowder as the explosive and ball bearings as additional shrapnel. The officials said that instructions on how to design such bombs are available on the Internet.
Obama, in an appearance in the White House briefing room, said it was not yet clear who carried out Monday's twin blasts that killed three people and sent 176 to hospitals with injuries, 17 critical.
"Any time bombs are used to target innocent civilians, it is an act of terror," Obama said. "What we don't yet know, however, is who carried out this attack or why, whether it was planned and executed by a terrorist organization - foreign or domestic - or was the act of a malevolent individual."