PHNOM PENH, Cambodia - One of the two co-investigating judges of Cambodia's UN-backed war crimes court, Frenchman Marcel Lemonde, said Thursday he was quitting his job at the tribunal to focus on other projects.

The announcement came as the court indicted four former senior Khmer Rouge leaders for genocide, war crimes and crimes against humanity.

Lemonde said he had joined the tribunal in 2006, intending to stay for just three years but he had ended up serving for four.

He said he was proud with what he had achieved in his role for the tribunal, despite frequent difficulties, but that he was now "passing the baton to someone else".

He plans to leave in early December.

"I have other longstanding plans that I cannot now ignore. I have informed (co-investigating) judge You Bunleng and my colleagues and so I would like to move on with my other plans."

Bunleng said his colleague's departure had not surprised him because he always knew Lemonde would only stay for a limited number of years.

He thanked the Frenchman for his commitment and for staying "with us until the closing order was finalised."

He added that he would work with Lemonde's successor to decide how to proceed with a possible third case against other former Khmer Rouge cadres.