I am looking for old story.
Starts with a college aged man stopping a young girl from riding into traffic.
He noticed girl was acting dull witted.
he called police.
Later Police told him that girl was kidnapped and hypnotized and bicycle was a bomb.
He goes on to help police break up the gang.
The story that I read, but like you forgot the title/author, a man goes to a bank, there is a bank robbery taking place, he sees a girl riding towards the robbers that are shooting. He stops the girl, is shot and ends up in a hospital. This lines up with your last two lines.
More of the story is he stays with a nurse with a young daughter, a junk yard, a fire at the junk yards house, and a daughter from a mafia family turning legal.
For others with better memory.
"FBI. They found the girl and the bike." I said and Theresa responded just as I had. "Don't worry, she's alive. That's what I thought, too. I don't know the whole story, but the bike she was riding was rigged as a bomb. Theresa, I could have been blown to bits."
Chapter 20 - Deciding Moment by John Smith
The girl's bicycle did have a bomb. The bank robbery gang used young kids on bike bombs to make their escape. I also suggest John Smith's Robin story.