Former Democratic presidential nominee Michael Dukakis says Donald TrumpDonald John TrumpTrump: 'Haven't thought about' pardons for Mueller target Pence: Rocket attack 'proves that Hamas is not a partner for peace' Conservation remains a core conservative principle MORE is "getting away with murder" by not releasing his tax returns.

“I think we’ve got to start talking about Trump, because this guy’s getting away with murder,” Dukakis said Thursday on CNN’s “New Day."

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"I mean, take, for example, the income tax returns. Look, this guy has got to produce his income tax returns.”

Dukakis, a former Massachusetts governor who ran for president in 1988, said voters should not accept the Republican presidential nominee's “absolute foolishness” about releasing his returns.

“He’s running for the presidency of the United States, and all he has to do is release them, and I think it’s pretty obvious that there’s something in there he doesn’t want released,” he said.

“But I think we’ve got to insist on this kind of stuff because no presidential candidate I’m aware of in the last, what, 30 years, has not done so,” added Dukakis.

Trump’s campaign chairman on Wednesday said the billionaire will not be releasing his taxes before the general presidential election.

“Mr. Trump has said that his taxes are under audit and he will not be releasing them,” Paul Manafort said.

“It has nothing to do with Russia; it has nothing to do with any country other than the United States and his normal tax auditing process.”

Conservative columnist George Will on Monday claimed Trump is keeping his tax documents hidden because they may show “he is deeply involved in dealing with Russian oligarchs.”

Trump has repeatedly pushed back against calls to release his tax returns, insisting the Internal Revenue Service (IRS) is auditing them.

The IRS, however, has said that nothing is preventing the real estate tycoon from making his tax background public.