The daughter of a man charged with killing her boyfriend has testified in Newfoundland Supreme Court against her father.

Penny Lockyer told a Corner Brook courtroom on Thursday that her father, Neil Lockyer, had become paranoid after suffering a brain injury in an industrial accident in 1989.

She told the jury that her father thought that her boyfriend, Frank McKay, was a spy for the workers' compensation system, and that officials were trying to cut off his benefits.

Neil Lockyer was charged with second-degree murder in the February 2006 stabbing death of McKay.

The defence does not dispute that Lockyer stabbed McKay, a former Nova Scotia resident, but maintains that he is not criminally responsible.

The prosecution opened its case by calling Penny Lockyer as its first witness.

She told the court that her father came to believe that he could not speak inside her house because he believed it was bugged. She said that her father had tried to get McKay to admit he was a spy.

At that point, she said, she went to the police and to a hospital to seek help. However, because her father had not actually done anything, she testified, she was turned away.

Several weeks later, Lockyer stabbed McKay with a large kitchen knife.

She said she tried to help McKay, but that her father punched her in the face. She took her two children and ran to a neighbour's house for help.

However, McKay was dead by the time that she returned.

Autopsy results released after McKay's death showed he died of multiple stab wounds.