Charan Chong-on and Chaiya-sith Lamoh worked as informants in return for meagre money after being arrested, and were later persuaded by police to infiltrate criminal gangs to obtain intelligence, a police source said yesterday.

Charan, the man seen wearing sunglasses in television news footage of Monday's melee, also served a local politician in Nakhon Si Thammarat's Tha Sala district before working as a canvasser for an MP in Surat Thani, his native province, where he worked as a rubber tapper.

Charan, who uses the alias "Parn", is a regular gambler and has been seen in several gambling dens, both in Bangkok and elsewhere, waging money despite a common belief that he is unemployed, the source said.

It is reported that he married a woman from his own neighbourhood in one of the grandest weddings in the area in recent years, before disappearing from his home to make headlines for his role in Monday's assault.

Charan was arrested in 1988 by Rat Burana police and again in 1993 by Bang Mod police for gambling. He was arrested in 1997 for selling 500 amphetamine tablets and having a firearm in his possession. The case was never pursued.

Chaiyasith was arrested in Bangkok on three occasions - in 1992, 1994 and 1998 - all three times on gambling charges.