For nearly three months, Barry Heitin, a 76-year-old retired lawyer, thought he was part of a government investigation that felt like something out of the movies. He was actually assisting criminals in stealing hundreds of thousands of dollars — of his own money.

Last fall, he spent just about every weekday doing the legwork and making withdrawals from his bank accounts as part of an intricate scam: He believed he was helping the feds safeguard his money and catch thieves who were after it.

“They kept telling me, ‘This is a big case and we are going to stop a whole ring of people,’” Mr. Heitin said. “It was like a rabbit hole. I was going down the hole with them.”

It cost him almost all of his retirement savings: roughly $740,000.

Americans spend a lot of energy saving for retirement and worrying about losing money to the gyrations of the stock market. But these days, sophisticated criminals — on dating sites, on social media, in messaging apps or using malicious software — present an ever-growing risk to people and their savings.

The nature of these schemes makes it nearly impossible to recover the money, leaving victims with little recourse. The stolen funds are often whisked to overseas accounts or laundered through cryptocurrency wallets, which are quickly emptied.

Mr. Heitin was one of many people interviewed by The New York Times who were ensnared in scams that could be so elaborate it’s as if they were created in a writer’s room testing different plot devices. Scammers can impersonate government officials, tech support staff or love interests. They coach victims on how to sidestep fraud prevention measures at financial institutions, and they use manipulative psychological tactics — isolation, a sense of urgency or preying on people’s willingness to trust or connect — to keep the scam going.

“The crime doesn’t end until they have taken all of your money,” said Erin West, a prosecutor with the district attorney’s office in Santa Clara, Calif., who leads a cybercrime task force. “It is going to hit every victim the same exact way until they lose everything they have, whether it is $5,000 or $50,000 or $15 million.”

Compounding the pain, there can even be a hefty tax bill waiting for them after they’ve drained their retirement accounts.

Potential losses from cybercrime exceeded $12.5 billion in 2023, a 22 percent jump from 2022, and more than triple the levels in 2019, according to the F.B.I.’s Internet Crime Complaint Center. But these figures underestimate the problem, since many victims don’t report their losses.

People over 60, often targeted by cybercriminals because they are viewed as having the largest piles of savings, experienced the steepest losses among all age groups in 2023, at more than $3.4 billion, according to the F.B.I.

Ensnared in a Fake Investigation

For Mr. Heitin, it began in September, when he was unable to log into his 401(k) retirement account. When he tried again several days later, he got in, but the screen quickly changed and instructed him to call the 401(k) provider’s fraud department. He called the number on the screen, which had the firm’s logo on it.

That’s when he connected with a man who called himself Charles Hunt and said he was a fraud investigation officer with the firm. (Mr. Heitin and his lawyer said they didn’t want to name the institutions because they were in discussions about possible restitution.)

Mr. Hunt told Mr. Heitin that someone was trying to gain access to his account.

Then, he named a big bank where Mr. Heitin held an I.R.A., as well as checking and savings accounts. That money was vulnerable, too, he was told. Mr. Hunt then connected him with a man who called himself Hayden Smith, who said he was with the bank where Mr. Heitin kept his checking account.

Mr. Smith said he had identified two $10,000 transactions for purchases of child sexual abuse imagery through a site in China. He peppered Mr. Heitin with questions. “Ever been to China? Know anyone in China? Buy anything in China?”

He had not. Next, Mr. Heitin was told that financial institutions often worked with the federal government on these cases. Would he be willing to talk with them?

That’s when a third man, who identified himself as Finn Whitrock, came on the line and said he was with the Internal Revenue Service. He provided a badge number and said that Mr. Heitin’s other accounts were at risk, but that the government could safeguard his money by transferring it to a federal locker.

If he was willing to cooperate with their investigation, Mr. Whitrock explained, Mr. Heitin could play a critical role in preventing a ring of criminals from preying on others — while ensuring he wouldn’t lose the $20,000 the thieves had tried to steal. But they needed to move quickly.