Another active member of the Sam Rainsy Party (SRP) was murdered Monday night in Koh Kong province.
The opposition party has not concluded whether or not the murder was politically motivated.
The SRP secretary general Eng Chhay Eang said on Monday night two men came to the victim's house and asked the victim permission to stay overnight at his house.
The victim first said no but later agreed to the request. He was shot to death a few moments later when he was leaving the house to register the guests with the village chief.
Koh Kong deputy police chief said his office has not yet been informed of the case but said he will investigate.