BANGKOK (AP) - Thai police on Wednesday (Dec 18) arrested a convicted serial killer who was accused of a fresh killing just seven months after his early release from prison.

Somkid Poompuang was arrested aboard a train after a nationwide manhunt launched when he was identified as a suspect in Sunday's killing of a hotel maid in the north-eastern province of Khon Kaen.

Somkid had been dubbed the "Jack the Ripper of Thailand" after being convicted in 2005 of killing five women who worked as nightclub entertainers and masseuses by strangling or drowning them.

He was freed in May this year in what prison officials now say they regard as a misguided policy regarding well-behaved convicts.

Police Colonel Khajornrit Wongrat, who is overseeing the investigation into Sunday's killing, said the woman, Ms Rasamee Mulichand, had met a man online and he had moved in to live with her earlier this month.

"She told her daughter and neighbours that she was going to marry the man on Dec 15, which was the day she died. The boyfriend went missing on the day, too," Col Khajornrit said.

Photos that Ms Rassamee posted on her Facebook page of her and her boyfriend led police to conclude that he might be Somkid, triggering a manhunt.

His photos and details were released to the public, with a reward of 50,000 baht (S$2,240) offered for information leading to his arrest, along with a warning that he is very dangerous.

A student couple on a train going from the north-east to Bangkok phoned police to tell them he was sitting near them, and he was arrested when the train made a scheduled stop.

Corrections Department director-general Narat Sawettanan said at a news conference that releasing Somkid was a mistake and he appointed a committee to consider a new policy for reducing the sentences of well-behaved inmates.