The FBI is offering a $5,000 reward for information that identifies an alleged bank robber whom authorities are calling the “silent bandit” following hold-ups at several central Maine banks in recent years.

In a news release Monday, the FBI said it was working with police in Skowhegan, Waterville and Pittsfield to identify the person linked with four bank robberies, each of which was reported in separate years during the winter.

“During each of the robberies, the suspect passed notes to the tellers, threatening violence and demanding cash,” the FBI Boston Division said in the release. “The ‘Silent’ Bandit has never spoken during any of the robberies and he has never displayed a weapon. Following each robbery, the suspect walked calmly away from the scene.”

The robber is described by authorities as a heavyset white man who is probably 55-65 years of old, height 5-foot, 6-inches to 5-foot, 10-inches tall. In each robbery he was wearing gloves; a long, dark, hooded, rain parka; and facial coverings, while in some robberies he was also seen wearing a “mad bomber”-style hat, the FBI said.

Kristen Setera, spokeswoman for the FBI, said authorities were now seeking the public’s help — more than two years after the last reported robbery — “because we have exhausted all of our investigative leads at this point in time, and the robberies remain unsolved.”

Authorities said they’ve linked the “silent bandit” to the following robberies:

Dec. 13, 2012, at 4:40 p.m., Franklin Savings Bank, 194 Madison Ave., Skowhegan.

Feb. 21, 2013, at 4:42 p.m., Key Bank, 305 Kennedy Memorial Drive, Waterville.

Feb. 7, 2014, at 2:45 p.m., Bangor Savings Bank, 108 Somerset Ave., Pittsfield.

Feb. 12, 2015, at 5:47 p.m., TD Bank, 182 Main St., Waterville.

The FBI said it was offering a reward of up to $5,000 for information “leading to the identification, arrest and prosecution of the person responsible for these robberies.”

“At this point in time we do not believe the ‘Silent’ Bandit is linked to any other bank robberies,” Setera said by email Monday, adding that authorities do not know why the robber has stopped the last two years. “The FBI came up with the moniker the ‘Silent’ Bandit because he has never spoken during any of the robberies.”

Waterville Police Chief Joseph Massey has previously said that the bank robbery cases are different from others, because the “frequency of the crimes and some other particularities lead us to believe that this isn’t a robber committing crimes to fuel a drug habit.”

“Frankly, once we know who is committing these robberies, we are very curious to learn why he is doing this,” Massey said in 2015, following the TD Bank robbery in Waterville. “We’ve considered many possibilities: stealing money to go on vacation, to pay taxes or some other debt or even to care for a sick family member. We aren’t ruling anything out.”

Authorities asked that anyone with information should call the FBI at 857-386-2000 or the Waterville Police Department at 1-207-680-4700. Tips can also be electronically submitted at tips.fbi.gov.