WATERVILLE — City officials are trying to solve a mystery involving a long-dead mayor, a bridge and a bronze plaque that disappeared many years ago from that bridge but recently was discovered in a basement.

The investigation into the mystery started several weeks ago when a man in a pickup truck drove into the Public Works Department complex on Wentworth Court with the 50-pound plaque, saying it was found in a house that was being razed. He did not leave his name or a location where the plaque was found, according to Public Works Director Mark Turner.

“Some guy just dropped it off,” Turner said. “They were tearing down a building, and he found it in the basement and thought he should return it to the city of Waterville.”

The 2-by-3-foot plaque reads, “Thayer Memorial Bridge, Erected 1934 by City of Waterville Civil Works Administration and Emergency Relief Administration, Hon. L. Eugene Thayer, administrator and mayor.”

It refers to former Waterville Mayor Lorenzo Eugene Thayer, who died Sept. 3, 1934, at 51 and is the only city mayor to have died while in office.

Not knowing what bridge the plaque belonged to, Turner, Public Works Operations Manager Bob Gilchrist and City Engineer Greg Brown started scouting around.

Turner discovered an indentation on the Gilman Street bridge that fit the shape and size of the plaque, which was oxidized and stained from being in a moist environment. Public Works mechanic Cary Collamore on his own time cleaned it up using a mild solvent and then air-blasted it with fine silica particles to remove surface buildup and stains. Then he applied a sealant to preserve the bronze finish.

More city officials got in on the act. City Planner Ann Beverage dug up an annual report from 1935 that spells out Waterville’s decision to rename the Gilman Street Bridge for Thayer after his death. He was a hard-working mayor who was in office during the Great Depression and was successful in re-establishing the city’s credit after banks had closed, the report said.

After Thayer’s death, city officials decided to rename the Gilman Street Bridge over Messalonskeee Stream “Thayer Memorial Bridge.”

Thayer, a Waterville native and Colby College graduate, also was one of the founders of the Morning Sentinel in 1904 and served as its business manager. He headed the local Federal Relief Administration, helping the needy and unemployed, and was affiliated with several insurance firms. He was a director of People’s National Bank.

A Democrat, he was elected mayor in 1933 and re-elected in 1934 by the largest majority in the city’s history, according to the story.

Turner surmises the bridge plaque was stolen many years ago.