SALEM, Ore. (AP) — The father of a Salem man accused of killing two Oregon law enforcement officers in a bank blast was arrested Tuesday on bomb-making conspiracy charges, authorities said.

Bruce Turnidge, 57, was arrested at a farm about 13 miles southwest of Salem, where his son, Joshua, lived.

Bruce Turnidge faces charges of conspiracy to manufacture and to possess an explosive device, the Marion County district attorney's office said.

Earlier in the day, Joshua Turnidge appeared in court briefly for the first time on charges that include aggravated murder, which could carry the death penalty if prosecutors seek it.

Law enforcement officers converged on the farm Tuesday and were searching it "from front to back," said Lt. Sheila Lorance of the Marion County sheriff's office. "We're searching all 750 acres." She would not say what for.

Bruce Turnidge is not the owner of the farm, but public records give it as his address. It was not clear whether he was a renter there, and the owner was not immediately available for comment.

Authorities have refused to say what they think was the motive for the bombing Friday at the West Coast Bank branch in Woodburn, an agricultural town north of Salem.

Like his son, Bruce Turnidge has a record of violations of traffic and vehicle laws, but no record of serious offenses in Oregon.

Joshua Turnidge, 32, a Navy veteran working in a biodiesel fuel enterprise with an uncle, is accused in the explosion last week that killed an Oregon State Police bomb technician and a Woodburn police officer as they were taking apart a device they believed to be a fake bomb.

The blast Friday killed Senior Trooper William Hakim and Woodburn Capt. Tom Tennant. It critically injured Woodburn Police Chief Scott Russell, who lost his right leg from the knee down, and his left leg was mutilated, said a probable cause statement released Tuesday.

The bomb — in a green metal box — had been left outside the bank. Hakim brought it inside after inspecting it with an X-ray scanner and determining it was a fake, according to the probable cause statement.

The box exploded as Hakim tried to open it and Tennant held it down, a bank employee told the investigator who wrote the probable cause statement.

About seven hours before the blast, a man called in a bomb threat to the Wells Fargo Bank in Woodburn, which is next door to the West Coast Bank branch, according to the statement.

The man said "if 'they' didn't leave the building, all of them would die," the court document states.

The man also said a cell phone would be found next to a garbage can, and that he would give further instructions on it. The man also said he would be calling the West Coast Bank.

Local police officers arrived at the Wells Fargo building, opened a garbage bin, and spotted a cell phone on top of what appeared to be a package. Hakim and an FBI bomb technician were called. They examined the package and cell phone, and determined it was a hoax device.

Woodburn police searched the area around the two banks for other devices, and a green metal box was spotted next to the West Coast Bank building.

Hakim, Tennant and Russell arrived at the West Coast Bank. After Hakim inspected and X-rayed the green box, he said he was "confident that it was a hoax device and that it could be taken apart to be placed into evidence."

The statement says a bank employee saw Hakim trying to open it while Tennant held it, and then it exploded.

Joshua Turnidge appeared in court Tuesday morning for the first time. He got a court-appointed attorney and did not enter a plea. His next scheduled court date is Dec. 26.

His father is to appear in court Thursday.

Investigators have not yet said whether they know of a motive.

Police believe Turnidge purchased two Tracfones, including the phone found at the Wells Fargo bank, at a Bend Wal-Mart on Nov. 26. Airtime cards for the phones were purchased at a Salem Wal-Mart on Dec. 11, the day before the bombing. The two phones were activated on the morning of the bank bombing, the court document states.

Police obtained surveillance video showing "the subject who bought the two Tracfone airtime cards" walking out of the Wal-Mart to a blue early 1980s Chevrolet pickup truck. Investigators were able to determine the truck is registered to a Bruce A. Turnidge.

Police Sgt. John Troncoso wrote in the document that Bruce Turnidge is too old to be the person in the surveillance video, but he discovered Bruce Turnidge is the father of a Joshua Turnidge. Troncoso looked at Joshua Turnidge's DMV photograph and recognized him as the man in the surveillance video.

This past Sunday, Troncoso and another officer drove by Turnidge's residence in Salem and spotted the blue pickup, and he was arrested.