A financial adviser who stole about $1.2 million from the retirement accounts of his mostly older victims, one of whom had dementia and another of whom had a traumatic brain injury, has been sentenced to 4 1/2 years in prison.

Paul McGonigle, 67, of Middleborough, starting in 2015 pretended to be his clients on calls with their annuity companies and signed their names on forms requesting withdrawals from their annuities, the U.S. attorney’s office in Boston said Wednesday.

He also induced victims to give him money to invest on their behalf, which he used for personal and business expenses, prosecutors said.

When clients began to ask questions, McGonigle concealed his fraud by assuring clients that their investments were growing, prosecutors said.

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"What Paul McGonigle did is despicable," Christopher DiMenna, acting Special Agent in Charge of the FBI's Boston office said in a statement. "He preyed on his elderly and vulnerable clients, betrayed their trust, and stole over $1.2 million from their retirement accounts."

Investment scams cost U.S. residents more than $3.3 billion last year, he said.

McGonigle was also ordered to pay restitution. He pleaded guilty in February to investment adviser fraud, money laundering, wire fraud, mail fraud and aggravated identity theft.