WINCHESTER, Mass. -- A serial bank robber has struck again.

NewsCenter 5's Jack Harper reported that a robbery task force is trying to figure out how to catch him. The robber has hit at least a dozen banks.

Police said he has been so successful because he blends in so well with other bank customers.

"He is very, very average looking, however somebody has to recognize him as, 'That's my roommate.' 'He lives in my neighborhood.' 'He works with me.' 'He goes to school with me.' Something along those lines," said Winchester police Lt. James Pierce.

Police said he has robbed banks all over the greater Boston area. On Monday, police said he hit a Somerville bank.

"Comparing the surveillance photos of this robbery with past robberies, he seems to be the same individual who has robbed 11 other banks in the greater Boston area," said Somerville police Lt. Paul Upton.

On Tuesday, 21 investigators from state, federal and local departments compared photos and notes on the robber.

"He just looks like the average, young guy. Could be standing right beside you in the bank, and if your weren't thinking about him, you would not know he was about to rob the bank," said Pierce.

Pierce said if people think they know who the robber is, they should contact local police.

So far, there have been no injuries during the incidents, but police fear the robberies could escalate to violence.