Investigators have spotted a Boston Marathon bombing suspect from security video taken before two blasts ripped through central Boston on Monday, a law enforcement source said on Wednesday, in what is potentially the biggest break in the case yet.

No arrests had been made, and the suspect in the video had not been identified by name, two government officials said. Police may make an appeal to the public for more information at a news conference scheduled for later on Wednesday, a government source said.

The explosions at the Boston Marathon finish line killed three people and injured 176 others in the worst attack on U.S. soil since September 11, 2001.