PORTLAND – A former partner in a prominent Portland law firm was sentenced Tuesday in Cumberland County Superior Court to 28 months in prison for stealing about $300,000 from his clients and the firm.

John Duncan, 54, of Falmouth will serve his felony theft sentence concurrently with the 28 months he received earlier this month in U.S. District Court for tax evasion.

At Tuesday’s sentencing, Justice Robert Crowley and Duncan’s attorney, Toby Dilworth, agreed that there was no satisfactory explanation as to why Duncan stole money from Verrill Dana over the past decade at a time when he was earning about $250,000 a year as a trusts and estates lawyer with the firm.

“If he had stolen this money to feed a gambling habit or a drug habit, then at least we’d know why he did it,” Crowley said. “We’re all left with the question of why.”

“He had an irrational insecurity about money,” Dilworth told the judge. He said his client has fully repaid the victims in the case, plus back taxes, and noted that the wide publicity surrounding the case has placed an extraordinary penalty on Duncan, his family and friends.

Duncan, who was disbarred permanently by the Maine Supreme Judicial Court, told the court that his remorse is “overwhelming.” He apologized to his family, friends, colleagues, law partners and the public, saying he was prepared to accept his sentence, serve his time and move on.

Duncan had joined Verrill Dana in 1978 after graduating from Bowdoin College and receiving a law degree from the University of Virginia.

He is expected to begin his sentence Oct. 1 at the Federal Detention Center in Brooklyn, N.Y.