Monday's terror attack on the Boston marathon claim the lives of 3 people - an 8-year-old boy, a young woman and another person yet to be identified - and injured 180 more.
The FBI is leading the investigation in the attempt to find out the culprit or culprits behind what President Obama called a "heinous and cowardly act."
Here's what CNN knows about the bombs:
- A knowledgeable source called the bombs "crude."
- The bombs appear to have been inside metal pressure cookers that were in backpacks, a federal law enforcement official with knowledge of the investigation told CNN.
- A law enforcement official said it was "likely, but not certain" that a timing device was used and that at least one of the bombs was not activated by a cell phone
A U.S. official tells CNN the explosive device was an IED with BBs as shrapnel and a pressure-cooker type device.
Erin Burnett spoke to Dr. Alasdair Conn, chief of emergency services at Massachusetts General Hospital about whether the authorities' account of shrapnel connected to the device consistent with the type of injuries he is seeing.
"We have a lot of the patients who have a lot injuries from these metallic fragments, which I think - I am not a ballistics expert, but I think were in the device," Dr. Conn said.
Erin Burnett has the latest tonight at 7p and 11p ET on CNN.