Boston is being terrorized by a series of seemingly random murders of women. Based on the true story, the film follows the investigators path through several leads before introducing the Strangler as a character. It is seen almost exclusively from the point of view of the investigators who have very few clues to build a case upon.

20th Century Fox originally hired Terence Rattigan to write the screenplay based on the book by Gerold Frank, but he wrote it as a comedy and was replaced by Edward Anhalt. In Rattigan's version, the killer was revealed, by a computer, to be Darryl F. Zanuck.

Capt. Ed Willis:
Everybody's banging everybody. It's a horny world.

Factual errors: In the film it is assumed DeSalvo was guilty, and it portrays him as suffering from multiple personality disorder and committing the murders while in a psychotic state. DeSalvo was never diagnosed with, or even suspected of having that disorder.

Music by John Philip Sousa
Heard from the television during the opening scene