The words "Grandpa" and "criminal" don't typically go together, but police are making an exception in the case of an older man who they believe has robbed six Oregon banks in the past half-year.

The words "Grandpa" and "criminal" don't typically go together, but police are making an exception in the case of an older man who they believe has robbed six Oregon banks in the past half-year.

The reward for the "Grandpa Bandit" — suspected of robbing a Medford bank on Thursday — has now hit $15,000.

Bank of America is offering a reward of up to $10,000, and the Oregon Financial Institutions Security Task Force is offering a reward of up to $5,000, for information leading to the arrest and conviction of the serial bank robber.

Suspected in five other robberies in Salem, Sherwood, West Linn and Hillsboro, the unknown man is believed to have robbed the Bank of America branch at 790 Stevens St. in Medford on Thursday. Five of the six banks he has robbed are Bank of America branches.

Although he did not show a weapon in the Medford robbery, he has threatened tellers in previous robberies. In one instance, investigators believe that he threatened to kill a teller as he showed her a weapon in his waistband.

Witnesses describe the man as a white male, between 5 feet 8 inches to 5 feet 10 inches tall, weighing between 160 to 180 pounds, with gray hair and hazel eyes. During the Medford robbery, he wore a khaki-colored vest, blue jeans and a baseball cap with a white circle-type logo.

Beth Anne Steele, a spokeswoman for the FBI's Portland office, told the Oregonian that the Grandpa Bandit "earned that nickname because he is older than your average bank robber." She said he's estimated to be in his 50s or possibly early 60s.

Anyone with information is asked to call the FBI in Medford at 541-773-2942.

FIST is a cooperative effort made up of representatives from banks, savings and loans, and credit unions, as well as representatives from local, state and federal law enforcement agencies.

In addition to the Medford robbery, the man is believed to have robbed the following banks in the past six months:

Oct. 14, 2009: Key Bank branch at 750 Lancaster Drive N.E. in Salem;Oct. 29, 2009: Bank of America branch at 3803 Center Street N.E. in Salem;Dec. 2, 2009: Bank of America branch at 15961 S.W. Tualatin-Sherwood Road in Sherwood;Dec. 10, 2009: Bank of America at 19181 Willamette Drive in West Linn;Dec. 22, 2009: Bank of America at 1375 N.W. 185th Ave. in Hillsboro.

Steele asks that anyone with information call the FBI in Medford at 541-773-2942, the FBI in Salem at 503-362-6601 during normal business hours or the FBI in Portland at 503-224-4181 24 hours a day.

Reach reporter Sanne Specht at 541-776-4497 or e-mail sspecht@mailtribune.com.