Three people are dead and over one hundred wounded after bombs blew up seconds apart at the finish line of the Boston Marathon.

Federal investigators are now trying to find out who is responsible.  The blasts raised fears of a terror attack .

President Barack Obama was careful not to use the words "terror" or "terrorism" as he spoke at the White House Monday after the deadly bombings, but an administration official said the bombings were being treated as an act of terrorism.

"We will find out who did this. We'll find out why they did this," the president said. "Any responsible individuals, any responsible groups, will feel the full weight of justice."

According to the AP, the FBI served  a warrant late Monday on a home in suburban Boston and appealed for any video, audio and still images taken by marathon spectators.

There were reactions of shock and horror across the US.  “Taste of Country” reports,   stars like Lady Antebellum, Scotty McCreery, the Band Perry and Lee Brice took to Twitter to send prayers to Boston.