The death toll from the bombings at the Boston Marathon has risen to three. More than 140 people are being treated at area hospitals for injuries, some of them grave and involving amputations.

There were two explosions around 2:50 p.m. in Copley Square near the finish line. The two explosions were timed about 14 seconds and took place about 100 yards apart on the same side of Boylston Street.

The FBI, with Special Agent Richard DesLauriers in charge, has taken the lead in the investigation. The FBI said the investigation is a “criminal investigation that is a potential terrorism investigation.”

Police said they have no suspects in custody. They have searched an apartment in Revere, a coastal city north of Boston. But police said Tuesday that the tenant, who is being treated at a hospital for burns, has been cleared and is not a suspect.

Police said they had no intelligence or indication prior to the race about a possible bombing.

President Obama called Governor Deval Patrick and Mayor Thomas Menino to offer assistance and condolences. He addressed the nation about 6:30 p.m. and said federal officials including the FBI and Homeland Security are working with city and state law enforcement. He said the people responsible and the reasons for the bombings remain unknown but that the government will find them and hold them accountable. He urged the public not to jump to conclusions.

“We don’t yet have all the answers. We still do not know who did this or why,” President Obama told the American people. “Any responsible individuals, any responsible groups will feel the full weight of justice.”

The Copley Square area was closed Monday night, although police were re-opening some surrounding streets to traffic this morning. Some businesses in the area have been affected.

Hartwig Safe

One of the spectators at the marathon was Dr. Robert Hartwig, president and economist with the Insurance Information Institute, who along with his wife had gone to witness their son finish the race.

Hartwig said his son finished the race about 1:15 p.m, well before the explosion around 2:50 pm. All of the Hartwigs escaped injury. While they were at the finishing line near the explosion scene when their son crossed the line, they had moved blocks away by the time of the explosion. He and his wife were in their car and his son was safe four blocks away.

Hartwig said the security he saw at the event was “enormous” with a heavy police presence as it should be for an event of this nature. The security included bomb-sniffing dogs that he saw early in the morning.

Hartwig said it is much too early to gauge any insurance effects of the incident. He did say that there did not appear to be a lot of property damage.

Officials said Boston will be under “heightened” law enforcement while the investigation continues. This will include random checks of subway passengers’ carry-on bags and knapsacks.

Monday evening, Boston Police Commissioner Ed Davis said law enforcement officers were still getting reports about possible suspicious packages.

“We are not at ease yet,” Davis said.

This morning in hearings on Capitol Hill, Defense Secretary Chuck Hagel became the first administration official to tie the bombings to terrorism, calling them a “cruel act of terror.”

Later in the morning, President Obama also referred to the attacks an “act of terrorism.”