SALEM, Ore. - A father and son were convicted yesterday of planting a bank bomb that killed two police officers in a botched robbery that prosecutors said had been motivated by plans to build a militia in case newly elected President Obama cracked down on the defendants' gun rights.

A Marion County Circuit Court jury found Bruce Turnidge and his son Joshua guilty on all 18 counts, which included aggravated murder, attempted aggravated murder and assault charges.

The convictions send the trial into a penalty phase that would begin today, when the jury will decide on life imprisonment or death row.

Kelly Mix, a brother-in-law of one of the officers killed, Woodburn police Lt. Tom Tennant, said that he was pleased with the verdict. "Look forward to having it behind us; not surprised by the outcome," added Mix, who said he attended the two-month trial regularly, except on days when he knew there would be graphic testimony.

The homemade bomb exploded at the West Coast Bank in Woodburn less than two weeks before Christmas 2008, killing a police bomb technician who was trying to dismantle it, as well as Tennant, who was helping. The town's police chief lost a leg in the explosion, which authorities said had been part of an attempt to rob the bank.

Prosecutors had presented evidence that the Turnidges harbored fantasies of building bombs, robbing banks and starting a militia. They needed money to keep their biodiesel company afloat, prosecutors said.

Witnesses testified that Bruce Turnidge, who grew up in a prominent farming family in the Willamette Valley but could not make a go of farming himself, wanted to live in a tent city with people who shared his political beliefs but couldn't get money to build an arms stockpile for a militia.

According to testimony, father and son exulted in the Oklahoma City bombing, and Bruce Turnidge viewed the bomber, Timothy McVeigh, as a hero. Prosecutors also said that both men believed that the Obama administration would crack down on their rights to own guns. The attack occurred about a month after Obama was elected.

The father and son turned against each other during the trial, but their attorneys came together to throw the blame for detonating the blast on State Police bomb technician William Hakim, who misidentified the green-painted metal box as a hoax.

A bank employee testified that Hakim was hammering and prying on the box when it exploded.

Prosecutors argued that a stray radio signal, perhaps from a passing trucker, activated a remote-controlled device that triggered the bomb.

Bruce Turnidge did not take the stand, but family members denied that he hated police or held extremist political views.

Prosecutors presented evidence that the Turnidges planted the bomb outside the West Coast Bank, then phoned in a threat to another bank next door, where they had left a cell phone and garbage bags to handle their demands for money. The bomb went unnoticed for hours.