A thug who held a teenager at knifepoint to blackmail his family for cash was snared by a half-eaten Wispa bar he left at the scene.
Mohammed Islam munched on the chocolate while holding the 18-year-old hostage at his house in Druids Heath, Birmingham, police said.
Officers identified him through traces of DNA from the half-eaten Wispa, which the victim managed to swipe after the three-hour ordeal.
DC Darran Ford, from Bournville CID, said: "I would like to pay tribute to the victim and his incredible presence of mind to grab the Wispa bar immediately before escaping.
"This played a crucial role in bringing Mohammed Islam to justice."
Islam lured the boy, who has not been named, to his address before holding a blade to his throat, slapping him around the head and threatening to kill him.
He forced the teenager's family to hand over hundreds of pounds in cash before finally letting his victim walk free, with a plastic bag over his head, on March 25.
Islam, 18, was jailed for eight years at Birmingham Crown Court on Friday for robbery, false imprisonment and blackmail, according to West Midlands Police.