A pet cockatoo killed while trying to protect its US owner from an attack provided enough crucial DNA evidence to convict the man's murderer.

The white-crested cockatoo, named Bird, belonged to a man in Dallas, Texas, who was killed on Christmas Eve 2001 by a former employee at his pool company.

Authorities said Daniel Torres - and another suspect due to stand trial - bound, stabbed, beat and slashed Kevin Butler after an argument, but during the struggle Bird flew at the pair, pecking them on the head and drawing blood.

Torres wiped the blood and then touched a light switch, leaving crucial DNA evidence at the crime scene, prosecutors said.

DNA evidence was also found on the cockatoo's beak and claws, and on two bloodstained knives found at the scene.

The combined evidence was enough to convict Torres of murder and sentence him to life in prison.

Bird 'spoke'

Bird paid the ultimate price for his bravery, as he was also found stabbed to death at the crime scene with his leg cut off.

Torres said in a confession he had stabbed the bird with a fork after it had pecked him "all over my head", the Associated Press news agency reported.

Defence lawyer Phillip Linder told the Dallas Morning News newspaper that he did not think the cockatoo played a major part in the jury's decision.

"I think that even without the bird - the crime scene, the photos and the way the victim was bound - it was a violent struggle [and] the state had a lot of evidence," he said.

However prosecuting lawyer George West said Bird's bravery had been key to the trial.

"This bird spoke; he spoke to us," Mr West told jurors at the trial.

We know this bird will attack anybody who is attacking his owner. And who did he attack? Daniel Torres."