LOS ANGELES — A Montana man who had homemade bombs in his house and is accused of shooting at a Kansas state trooper is a bank robber the FBI dubbed "the AK-47 bandit" and is suspected of holding up at least six banks in five states, authorities said Tuesday.

Richard Gathercole of Roundup, Montana, was arrested last week in Nebraska, said Stephen Woolery, a special agent in charge at the FBI's field office in Los Angeles.

Gathercole, 39, is suspected of committing six bank robberies and attempting another in California, Washington, Idaho, Nebraska and Iowa since 2012, Woolery said.

Richard Gathercole of Roundup, Montana. FBI via AP

FBI officials have been looking for years for the man they called the "AK-47 Bandit," who typically wore a balaclava mask and carried an AK-47 rifle with a drum magazine during the robberies.

Investigators believe Gathercole's first robbery was on Feb. 29, 2012 in Chino, California.

After robbing the California Bank & Trust, Gathercole, carrying an AK-47 rifle, opened fire on a Chino police officer who was outside, said Chino Police Chief Karen Comstock. The officer was seriously injured, but has since recovered and returned to the force, Comstock said.

Gathercole was arrested after he shot at a Kansas state trooper who was trying to pull him over last week. The trooper wasn't injured.

A suspect known as the AK-47 Bandit appears in surveillance video. FBI via AP

A jailhouse phone call transcript showed Gathercole asked his mother to clear his home of guns after his arrest. Investigators searched the home in the town of Roundup, Montana, about 50 miles (80 kilometers) north of Billings, on Saturday and found "numerous" improvised explosive devices, authorities said.

Gathercole is being held on state theft and possession of stolen firearms charges in Nebraska, and Woolery said federal charges were pending against him.

Prosecutors in San Bernardino County, California, said they planned to file a charge of attempted murder of a peace officer against Gathercole in connection with the 2012 shooting.

It was not immediately clear if Gathercole had an attorney who could comment on the allegations.