11/13/2014 11:56 EST | Updated 01/13/2015 05:59 EST

Robert Balbar, Accused Of Killing Girlfriend, Begins Murder Trial

KAMLOOPS, B.C. - A Kamloops jury has viewed video of a man telling an undercover police officer that he bashed his girlfriend on the head upwards of 60 times with a mallet and sledgehammer before packing her body in a cooler.

Robert Balbar's trial was opened Wednesday by prosecutors who played a secretly-taped recording of the man saying he repeatedly struck his girlfriend when she began waving around a machete, and then stowed away her body to avoid splattering the apartment with blood.

Balbar, 42, has pleaded not guilty to second-degree murder in the death of Heather Hamill, whose body was found in the North Thompson River in 2003.

Court heard the video confession was obtained during a so-called Mr. Big police sting operation, which involves police posing as criminals to gather information.