What is the name of the bomber in "Source Code"?

The bomber in Source Code is named Derek Frost.

Frost is responsible for bombing the commuter train that serves as the central disaster in the 2011 science-fiction thriller. He also plans a larger attack in Chicago involving a radioactive device hidden in a van. Identifying him is the main investigative objective assigned to Captain Colter Stevens inside the experimental Source Code program.

Stevens repeatedly relives the final eight minutes before the train explodes. Each cycle allows him to gather more clues, test suspects, and reconstruct Frost’s plan. The repeated timeline is not time travel in the conventional sense; it is a simulated reconstruction designed to help investigators identify the bomber and prevent a future attack.

Derek Frost is played by Michael Arden. A frequent mix-up is confusing Frost with Colter Stevens, the protagonist, or Sean Fentress, whose identity Stevens occupies during the simulation. Frost is the antagonist and the person behind the bombing plot.