A 27-year man was arrested at Hiriwadunna, Habarana for killing his mistress on Sunday.
He was taking her body in a mini truck presumably for disposal at the time of his arrest.
The victim, K. D. Kanchana Dilrukshi (28), was a mother of one.
She had been cohabiting with the suspect, police said.
The suspect, a resident of Sinhagama, Habarana, had lived together with 12 mistresses including the victim since his wife left him a few years ago, unable to bear frequent beating at his hands, police said.
Eleven of his mistresses had also fled due to domestic violence and he had beaten the last one to death following a heated argument, investigators told The Island.
Neighbours of the suspect said they had seen him beating the victim mercilessly, but they had not intervened to save her as they feared him.
After he had put her into his truck and driven away, one of the neighbours alerted the Habarana police, who put up roadblocks.
The suspect sped away without heeding orders to stop and police gave chase and stopped him at Hiriwaduna.
Upon being questioned, the suspect said the victim was his wife and he was taking her to hospital as she was not well.
But, he had already driven past the hospital in the area.
Police took him into custody.
Police said the suspect would be produced before courts soon.