Mr. Heastie appears to lead a relatively modest life. He lives in a single-family house in the Edenwald section of the Bronx that he bought for $440,000 in 2005. He earns a base salary of $79,500 as a legislator and an extra $14,000 as the Labor Committee chairman. He is also an adjunct professor of American government at Monroe College in the Bronx, which pays $5,000 a year.

On top of his legislative salary, Mr. Heastie claimed $23,440 in per diems and travel reimbursements in 2014, the third-most of anyone in the Assembly, the state comptroller’s office says.

He has just two stocks in his portfolio, both of which were bought in recent years: the Hong Kong Television Network and Medidata Solutions, a technology company that helps drug developers manage clinical trials. He has profited from both, but a spokesman said he had lost money on other stocks recently, including JetBlue and Priceline.

Image Joseph D. Morelle, the majority leader, backs Mr. Heastie. Credit... Nathaniel Brooks for The New York Times

Mr. Heastie also has $20,000 to $50,000 in credit card debt, according to a public filing that covers 2013. In addition, he consolidated less than $20,000 in other debt with Lending Club, a company that caters to people looking to refinance credit-card balances or other expensive loans.

It was Mr. Heastie’s campaign-finance reports that caught the attention of the Moreland investigators. There is little oversight on the spending of campaign funds, and some politicians use their campaign accounts to finance almost every aspect of their lives. Candidates are not required to itemize expenses less than $50, and commission investigators suspected that some lawmakers were exploiting that exception to mask improper spending.

An internal memorandum prepared by the Moreland staff cited Mr. Heastie among 28 lawmakers — out of the 213-seat Legislature — whose campaign reports from 2008 to 2013 showed more than $10,000 in spending that was not detailed. The memo said the failure to identify recipients or itemize credit-card payments “raises questions about whether campaign funds are being used for personal expenses instead of permissible election purposes.”