VANCOUVER �?A man accused of killing two teenage girls 30 years ago was found guilty of first-degree murder Saturday in a case that included stomach-churning details about the grisly stabbings.

The verdict carries an automatic sentence of life in prison with no parole eligibility for 25 years.

As the decision was announced, Robert Bonisteel sat in the prisoner's box with his head in his hands, then turned to his lawyer and raised his arms in exasperation as he was escorted out of the courtroom.

A B.C. Supreme Court jury deliberated for three days before reaching the verdict.

Bonisteel was a suspect from the beginning in the murders of Judy Mariea Dick and her friend Elizabeth Zeschner, both 14.

The girls' bodies were found in a garbage dump in suburban Richmond on Feb. 6, 1975.

During the nine-week trial, jurors watched a videotaped confession Bonisteel gave to undercover police in October 2002 in which he provided intricate details about how he picked up the girls in his car and killed them.

Besides the confession, which Bonisteel maintained was coerced, the Crown provided DNA evidence that linked him to the crime.

But Justice Al Stewart instructed the jury to consider the validity of DNA tests from evidence collected three decades ago because no one thought about how best to handle such samples so long ago.

It wasn't until a 2001 DNA test that blood found on Bonisteel's left shoe was matched to Dick.<

A forensic expert for the Crown testified that the probability that it belonged to someone other than her was one in 14 billion.

But the defence expert testified that the DNA removed from the shoe was unreliable for testing due to the small size of the sample. The expert also said the sample was subject to contamination due to improper handling.

DNA, or deoxyribonucleic acid, is the genetic blueprint in all human cells.

Dick and Zeschner, who considered themselves sisters, had gone to the store the day they disappeared.

Bonisteel confessed that he picked the girls up in his car and knew right away that he wanted to kill them just to know what that would feel like.

He also said he was trying to deal with the pain of his failing marriage, although his former wife testified the couple weren't having any problems.

Bonisteel said he drove the teens to a dumpsite and had them in the back seat, where they thought he would rape them.

He said he kissed Dick, "the pretty one,'' and stabbed her in the side, leaving the hunting knife in for five minutes. When he took it out, blood gushed out like a fountain, Bonisteel confessed.

He said Zeschner, "the adventurer,'' was scared and that he ordered her into the front seat and told her she'd be OK if she just did what he told her.

But he stabbed her too, up the left side and across the ribcage and then the throat, killing her instantly, he said.

Bonisteel said he then dragged the girls out of his car by their feet and left them in the tall, dead grass, where they would be well hidden.

Crown lawyer Hank Reiner said in his closing argument that Bonisteel simply knew too many details that only the killer would know, including the types of clothes the teens were wearing.

The jury heard that Bonisteel fled town the day after the girls' bodies were found, leaving behind his wife and five-week-old son.

On his way to Winnipeg, Bonisteel raped two women and spent 20 years in jail for the assaults.

Once he was out, undercover police posing as gangsters staged an elaborate sting operation to lure him with a promise of $80,000 in cash and elicited a confession.

Besides the DNA precautions Stewart gave jurors in his instructions, he also asked them to consider the number of mistakes Bonisteel made in describing significant elements of the crime.

"He gets things wrong, including the number of stab wounds, which the killer would never get wrong, never,'' Stewart said.

But Reiner told the jury in his closing arguments that Bonisteel made mistakes even about the most significant events in his life.

For example, he said his son was born in 1972, although the year was actually 1974.