Earlier, CBS News senior correspondent John Miller said authorities were questioning a Saudi national, who was under guard at an area hospital.
He was seen running from the explosion, and a civilian chased him down and tackled him. He was turned over to Boston police and was interviewed by the FBI.
Local and federal agents are now saying the man is not a suspect in the marathon bombings.
CBS News has confirmed that the Revere apartment officials raided Monday night is the home of a spectator and not a suspect. One of the men who lives at the residence told reporters, including CBS 2’s Young, that the man who was being looked at got hurt by the bomb and had nothing to do with the blasts. The Saudi man originally mentioned, related to the investigation, is not a suspect.
“Bottom line – this is going to take some time,” the man’s roommate said.
The fiery explosions took place about 10 seconds and about 100 yards apart, knocking spectators and at least one runner off their feet, shattering windows and sending dense plumes of smoke rising over the street and through the fluttering national flags lining the route.
Blood stained the pavement, and huge shards were missing from window panes as high as three stories. Victims suffered broken bones, shrapnel wounds and ruptured eardrums.
Davis said there were 176 casualties at hospitals, at least 17 of whom were critically injured. At least eight children were being treated at hospitals.
Three people were killed in the attack. So far, two of the victims have been identified. The third victim has been identified as a Boston University graduate student whose name is being withheld by the university until family notification.
That victim was also a Chinese national, and a woman, according to the Consulate General of the People’s Republic of China. The consulate also declined to identify the victim.
Martin Richard, 8, was watching Monday’s race and had gone to get ice cream before returning to the area near the finish line before the blasts.
On Tuesday, authorities identified the second victim as 29-year-old Krystle Campbell of Arlington, CBS 2 has learned.
William Campbell said his daughter was “very caring, very loving person, and was daddy’s little girl” and that the loss has devastated the family, the Associated Press reported.
Campbell’s mother, Patty Campbell, spoke to reporters on Tuesday afternoon, and expressed her distress and devastation.
“We are heartbroken at the death of our daughter…she was a wonderful person,” Patty Campbell said. “Everybody that knew her, loved her.”
The victim’s mother added “You couldn’t ask for a better daughter…I can’t believe this has happened. This doesn’t make any sense.”
A growing memorial for the victims of the attack was set up Tuesday night, CBS 2 reported.
The Boston Marathon is one of the world’s oldest and most prestigious races and about 23,000 runners participated. The race honored the victims of the Newtown, Conn., shooting with a special mile marker in Monday’s race.
Boston Athletic Association president Joanne Flaminio previously said there was “special significance” to the fact that the race is 26.2 miles long and 26 people died at Sandy Hook Elementary School.
The bombings occurred about four hours into the race and two hours after the men’s winner crossed the finish line. By that point, more than 17,000 of the athletes had finished the marathon, but thousands more were still running.
Spectator Cherie Falgoust was waiting for her husband, who was running the race.
“I was expecting my husband any minute,” she said. “I don’t know what this building is … it just blew. Just a big bomb, a loud boom, and then glass everywhere. Something hit my head. I don’t know what it was. I just ducked.”
Across the U.S. and around the globe, police have tightened security, monitoring landmarks, government buildings, transit hubs and sporting events.
In New York City, police have stepped up security at city landmarks, hotels, subway stations, transit facilities and other prominent landmarks.
Bloomberg said Tuesday the measures will stay in place until authorities know more about what happened in Boston.
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