When he saw a man he knew back in prison drinking with others in a Geylang coffee shop, he accused the man of being a "hantu".
Hantu is Malay for ghost, but is also prison slang for someone who is untrustworthy and an informer.
Odd-job labourer Jamsari Yusof, 51, was angry with Mr Gunasekaran Rengasamy, 43, for reporting him to a supervisor in Changi Prison.
When Mr Gunasekaran, who was jobless, denied the allegations, Jamsari became angier and a fight broke out.
During the altercation, Jamsari fatally stabbed Mr Gunasekaran on his face, neck and chest with a foldable knife.
Jamsari was jailed for 12 years yesterday after pleading guilty to culpable homicide not amounting to murder.
The court was told that Mr Gunasekaran and a friend, Mr Julius Pereira, 58, went to a coffee shop at Geylang Road at about 2am on Feb 13, 2012.. They joined three men, Redzuan Pupon, 40, Terrence Goh Chye Huat, 45, and Kung Kwai Cheong, 55, who were drinking at a table. When Jamsari was walking past, he saw Mr Gunasekaran and confronted him. It was the first time he had seen Mr Gunasekaran since their release from prison.
After helping himself to some beer on the table, he accused Mr Gunasekaran of being a snitch and the situation soon turned violent as Redzuan and Goh joined Jamsari in assaulting Mr Gunasekaran.
Deputy Public Prosecutor (DPP) Puspha S. said: "It is both shocking and sad that the very people whom (Mr Gunasekaran) was sharing a table with and drinking together turned against him once (Jamsari) entered the scene."
Jamsari's lawyer, Mr Mohamed Muzammil Mohamed, said his client knew Redzuan, Goh and Kung as they occasionally met at Geylang coffee shops.