A truck driver accused of killing a couple on their Wells County farm had handwritten directions to their home and owned a gun that matched a bullet from the crime scene, court records say.

Aron Nichols, 28, of Fargo, faces two counts of Class AA felony murder. Southeast District Judge James Bekken set Nichols' bail at $1 million cash on Monday and set a preliminary hearing for May 31.

Nichols is accused of killing Donald Willey, 70, and his wife, Alice, 67, on their farm near Sykeston. Their bodies, and their dead dog, were found in their home April 7, after it was destroyed by fire. An autopsy determined the Willeys were shot to death before the blaze.

Nichols had purchased a .45-caliber handgun at an East Grand Forks, Minn., store, court records said. He fired a gun on the property of his fiancee's father less than five hours after the fire at the Willey farm had been reported, authorities said.

Nichols' fiancee's father, Ronald Sorenson, showed officers where Nichols had been shooting on the property, and authorities matched a bullet from the Sorenson property with one from Alice Willey's body, the court documents said.

Nichols first denied owning a .45-caliber handgun, but later told authorities he sold it to an "unknown" man at a truck stop on April 13, the court records said.

Authorities also said they interviewed a trucking company worker who said Nichols had talked about going to a farm to kill "older people" who were relatives of his fiancee's daughter.

Nichols' court-appointed attorney, Lori Weisz, did not return telephone calls seeking comment on Monday.

"I feel there is probable cause," said Wells County State's Attorney Kathleen Trosen, who is prosecuting the case. She declined further comment.

Court documents say a search of Nichols' Fargo home and his pickup also turned up a coat that may have been damaged by heat, as well as handwritten directions to the Willey home, two hand-drawn pictures of the home, Mason jars filled with a "crystalline substance" and gasoline.

Investigators said they also found a sawed-off shotgun, a fully automatic rifle and a notebook with handwritten notes describing "fire behavior."

Nichols' fiancee's daughter is the Willeys' granddaughter. Authorities said the child is the daughter of Tamara Sorenson and her former boyfriend, Andrew Willey, who was killed in a helicopter crash in 2002 while he was working as a paramedic in Aberdeen, S.D.

Tamara Sorenson's daughter, who is 7 years old, was awarded $2.2 million, in a lawsuit filed against the helicopter manufacturer, the court records said. The trust for the girl was handled by Sorenson, Donald Willey and his son, Joel Willey, and an Aberdeen, S.D., bank official.

Tamara Sorenson, who lives with Nichols, has custody of the child. She and the Willeys had been embroiled in a bitter visitation dispute, and she stopped allowing the Willeys to visit the child in April 2006, court records said.

In February, an East Central District Court judge awarded visitation rights to the Willeys.

Trosen would not say Monday if Sorenson also is a suspect, but she said Sorenson had not been arrested.

Nichols was arrested last week on a felony charge of possessing a short-barrel shotgun, after a search of the Fargo home he shares with Sorenson, Trosen said.

The Willeys were known for their volunteer work in Sykeston and Carrington, and they were emergency medical workers for 20 years. Donald Willey was a retired volunteer firefighter.