SEATTLE -- FBI agents investigating a series of bank robberies in the Portland area have expanded their search after the so-called River Rat robber apparently struck in Puyallup and Auburn.

On Friday, an armed man entered the Northwest Commercial bank on A Street in Auburn, demanded cash and fled.

The man is also believed to be responsible for a robbery at Columbia State Bank in Puyallup on Aug. 24.

In an FBI news release issued Wednesday, agents said the man appears to be unconcerned about surveillance photos showing him in the Portland-area heists, leading investigators to wonder whether he lives in Western Washington and travels to the Portland area to commit the crimes.

Investigators gave the man the nickname "River Rat" because he robbed banks on both sides of the Columbia River.

Agents said they hope a friend, co-worker, family member or acquaintance will recognize him and report him.

The banking industry in Washington and Oregon is offering an award of up to $15,000 for information leading to his arrest and conviction.

Witnesses said the man is white, in his 20s to mid-30s, about 5 feet 7 inches tall, weighs 165 pounds with a medium build. He speaks with an accent.

The man sometimes wears a black athletic-style jacket with a white stripe or a gray zip-up sweatshirt, a baseball cap (sometimes camouflage), dark sunglasses and latex gloves.

The FBI said no one has been hurt in any of the eight robberies he's suspect of committing, but the man should be considered armed and dangerous.

Anyone with a tip should call the FBI at 503-224-4181 in Portland, the FBI in Seattle at 206-622-0460 or Detective Scott Smith at the Vancouver Police Department at 360-487-7416.