Just because a man is 83 and recovering from hip surgery doesn't mean he's not dangerous.

William Leo McDougall was so fed up with 94-year-old Mahn Van Nguyen singing in Vietnamese that he grabbed a wooden rod from the closet and hit him repeatedly in the head.

Both men were recovering from surgery at the Palm Terrace Healthcare Center in Laguna Woods. A nurse intervened but Nguyen later died from the trauma he endured.

McDougall was convicted Friday for the 2010 murder. He will be sentenced on October 26.

[Image via Shutterstock]