A man who stepped out of a pickup truck and started shooting at approaching police in Alaska was carrying two guns and about 400 rounds of ammunition on his body and in his truck, police said.

Matthew Stover also was wearing body armor and a bulletproof mask when four Fairbanks officers returned fire, killing him, Police Chief Erik Jewkes said at a news conference late Tuesday.

No officers were injured.

Jewkes appealed to the public for information about a motive and what must have been Stover's considerable preparations for an armed confrontation.

"We're all looking for answers. Why did this happen? What was his intent? What was he after?" Jewkes said. "Someone out there knows and may or may not want to say."

Stover, 21, of Northway, a village near Alaska's border with Canada, apparently had no previous contact with Fairbanks police, Jewkes said.

The incident began around 3 a.m. Monday when a witness saw a man with a mask and a rifle in the parking lot of a restaurant. The witness spoke to an employee who called 911.

Responding officers could not find the man but alerted staff at Fairbanks Correctional Center, the regional jail and prison, two blocks from the restaurant.

About a half-hour later, as police searched, corrections staff called to report a man with a long gun getting out of a pickup truck parked at a lot used over the winter for snow storage.

The lot is an easy walk from the jail, an ice arena and health facilities including Fairbanks Memorial Hospital.

Five officers approached the truck. From about 100 yards (91 meters), two officers activated lights on their patrol cars and called out with a public address system.

"As soon as that PA announcement started, the suspect exited the vehicle, immediately turned and started running toward the officers, raised an AR-style rifle and began firing as he ran toward the patrol cars," Jewkes said.

Four of the five officers fired back, killing Stover. Along with the rifle, he was carrying a 9mm handgun.

The pickup had been modified to disguise its make, Jewkes said.

When officers smelled camp stove fuel and saw a large bag outside the truck, they called in bomb experts from Fort Wainwright Army Post. They found no explosives.