The Senate Ethics Committee is pushing ahead with its investigation of Sen. John Ensign (R-Nev.) despite his announcement that he would resign, an unusual move that, legal observers said, demonstrates the panel’s resolve to at least issue a public rebuke.

With Ensign out of the Senate effective May 3, the committee will lose jurisdiction in the case and cannot formally charge him with wrongdoing in its 22-month investigation into Ensign’s handling of the fallout from an affair with a political aide. Late Thursday night, several hours after Ensign said he would resign, the top senators on the committee said he had made “the appropriate decision” but that their work would go on.

“The Senate Ethics Committee has worked diligently for 22 months on this matter and will complete its work in a timely fashion,” Sens. Barbara Boxer (D-Calif.), chairman of the panel, and ranking member Johnny Isakson (R-Ga.) said in a statement. The senators are traveling together through China as part of a 10-senator delegation.

Since June 2009, the committee has been reviewing Ensign’s affair with Cynthia Hampton, his former political treasurer, and his decision to dismiss her and her husband, Doug Hampton, who served in his legislative office until the firings in 2008. Ensign’s parents then gave $96,000 to the Hamptons in gift money, and the senator also helped Doug Hampton land lobbying work with his political supporters back in Las Vegas.

Legal experts could not think of a case in recent decades in which either the Senate or House ethics committees continued their work and issued a report after a lawmaker had left office. The Ethics Committee has several options, including releasing a short statement summarizing the case or a more detailed statement that could include allegations of violations by Ensign.

Another possible route would be to send the evidence and testimony gathered in the case to the Justice Department, which has been conducting a parallel criminal inquiry. “They don’t lose the jurisdiction to make a referral,” ethics lawyer Stanley Brand said Friday.

Ensign could have been in a legal vise grip. In his resignation statement Thursday, Ensign cited “further rounds of investigation, depositions, drawn out proceedings, or especially public hearings” as his rationale for quitting to spare his family from further public humiliation.

However, during an investigation of a different lawmaker, the D.C. Circuit Court of Appeals ruled in 2009 that testimony from a House member before its ethics panel could be sent to Justice for a criminal case, although the judicial panel was not unanimous in the case.

Earlier this year Ensign released a statement saying the Justice Department had ended the criminal investigation into his case, although Justice has never publicly confirmed that. Last month federal prosecutors brought charges against Doug Hampton, accusing him of violating federal laws that required him to not lobby Ensign for a year after leaving his office.

Prosecutors were likely to have a keen interest in whatever Ensign told the committee while under oath. Now that testimony will never take place.

Ensign’s attorney, Robert Walker, declined to comment on the case, as did Ethics Committee staff members. The Justice Department declined to comment.

Doug Hampton has alleged in media interviews that the $96,000 was severance pay, not a gift, and has said that Ensign knew Hampton was lobbying during what should have been his cooling-off period. Prosecutions for violations of the federal lobbying restrictions are rare, but associates of infamous lobbyist Jack Abramoff pleaded guilty to violating their cooling-off period. In addition, among other crimes, former representative Robert Ney (R-Ohio) pleaded guilty to helping Abramoff’s associates violate those lobbying laws.

Before the affair became public, Hampton and Ensign tried to come to an additional seven-figure settlement, which was being negotiated by Sen. Tom Coburn (R-Okla.), a close friend of Ensign’s and a former roommate in a Capitol Hill townhouse.

Those talks fell apart, and Hampton began contacting media outlets about the affair, prompting the once-rising Nevada political star to fly home and announce the affair himself. He resigned from his GOP leadership post, and, after trying to start a re-election campaign, gave up that effort last month.

Ethics watchdogs said Friday that Boxer and Isakson must make some public accounting for the work they have done behind closed doors. “It is critically important that the Ethics Committee follow through on their statement to complete this investigation so that the accurate, complete story can be made public. Otherwise, the mud will have been swept under the rug,” Meredith McGehee, policy director for the Campaign Legal Center, said.