An ethics probe commissioned by the D.C. Council into its longest-serving member, Jack Evans (D-Ward 2), is delayed because key witnesses have refused to speak to investigators, Council Chairman Phil Mendelson (D) said Monday.

The council voted in July to hire the law firm O’Melveny & Myers to conduct the investigation, one of several probes into Evans’s actions as a public official and as a private consultant.

But some of Evans’s clients have refused to talk to the firm and comply with subpoenas issued by it, Mendelson said during a news conference.

Investigators have spoken to Evans and one other person, the chairman said. Another witness has an interview scheduled later in the month, Mendelson said.

The D.C. Council is scheduled to vote Tuesday on legislation that would give the city authority to petition the D.C. Superior Court to enforce the subpoenas.

“There’s a great deal of public unhappiness with regards to Mr. Evans’s conduct, and the investigation needs to be completed now,” Mendelson said. “This needs to move more quickly, and the fault here is the interviewees who are not coming in to be interviewed.”

Mendelson hoped that investigators would finish most of their work during the council’s summer recess and release their findings soon after. Now Mendelson says the report’s release will be delayed until at least mid-October.

Mark Tuohey, a lawyer representing Evans, said his client was cooperating.

“Jack has thoroughly cooperated with the Council investigation from the moment it started, including providing any document requested and sitting for multiple interviews,” Tuohey said in a statement. “He will continue to do so and is confident that a thorough and objective investigation would conclude he tried to conduct his official and business duties properly and according to the rules.”

Evans told council colleagues in July that investigations will show his “actions — while not becoming — are far from that which has been reported or suggested.”

The lawmaker, who formed his NSE consulting firm in 2016, has not been charged with a crime.

“We are going to look at letting this continue to linger and linger and linger into next year,” said D.C. Council member David Grosso (I-At Large), who has urged Evans to resign. “I don’t think that’s good for the institution, and I don’t think the people of the District of Columbia deserve this.”

At least one NSE client, Forge, the parent company of Colonial Parking, confirmed its cooperation with the council investigation.

“Forge is fully cooperating with the council’s review of Mr. Evans’s conduct, including providing documents as requested and agreeing to meet with the council’s lawyers to discuss these matters,” said Kevin Byrd, the company’s general counsel.

Other NSE clients did not respond to requests for comment or declined to comment.

They include local development firms WillCo and EastBanc, the regional Eagle Bank and Fischer Holdings, a real estate investment firm. Another client is Digi Outdoor Media, a digital sign company whose founder had offered $50,000 to Evans’s consulting firm, along with 200,000 shares of stock and a paid summer internship for the lawmaker’s son. Evans has said he returned the money and stock and his son declined the internship.

Evans, who was first elected in 1991, is also facing a federal grand jury investigation.

Federal prosecutors subpoenaed records from the D.C. city government involving Evans and his business clients. FBI agents searched Evans’s Georgetown home in June.

Evans used his government email account to send proposals to prospective employers in 2015 and 2018, in which he touted his influence and connections as an elected official and board chairman of the Washington Metropolitan Area Transit Authority.

The District’s Board of Ethics and Government Accountability fined Evans $20,000 over his use of government emails, holding them up as evidence that he used government resources and the prestige of office for personal gain.

The emails also prompted the transit authority to launch its own investigation into Evans and his tenure there.

A law firm retained by Metro concluded that Evans “knowingly” and repeatedly abused his position at the transit agency to help friends and private clients.

The Metro board’s ethics committee agreed to find one violation: that Evans failed to disclose a conflict of interest with the parking company that was secretly paying him $50,000 a year. Evans and Corbett Price, the District’s other representative on the board, tried to keep this finding from becoming public, and both resigned in the fallout from the ethics probe.

The results of the Metro probe prompted the D.C. Council to strip Evans of his committee chairmanship and pursue its own investigation.

An earlier investigation by The Washington Post identified several instances in which Evans used his legislative position in ways that could benefit his clients.

Steve Thompson contributed to this report.