Updated at 4:56 p.m. ET

The Senate Ethics Committee has found "substantial credible evidence" that Republican John Ensign violated laws and Senate rules.

Chairwoman Barbara Boxer, D-Calif., announced that the committee is referring its findings to the U.S. Justice Department and the Federal Election Commission for further action.

The report's release caps a two-year saga that has already caused Ensign, once a rising GOP star who was talked about as a potential presidential candidate, to resign from the Senate. He stepped down the day before he was scheduled to be questioned under oath by the ethics investigators, and apologized to his colleagues for being "arrogant."

In 2009, Ensign admitted that he had an affair with Cynthia Hampton, a former aide whose husband, Doug, also worked as a top aide for the Nevada senator. It was later revealed that Ensign's parents paid the Hamptons $96,000 after Doug Hampton left his job in the senator's office.

Doug Hampton has been indicted for violating federal conflict-of-interest of laws, stemming from the Senate's rule banning ex-employees from lobbying the Senate for one year after employment. Ensign's lawyers said in December that federal prosecutors had cleared him.

Ensign's lawyers sent a 12-page letter to the ethics committee on Wednesday, detailing the Republican's response to the investigation.

"Sen. Ensign has admitted and apologized for his conduct and imposed on himself the highest sanction of resignation. But this is not the same as agreeing that he did or intended to violate any laws or rules," his lawyers, Robert Walker and Abbe Lowell, said in a statement.

The Senate Ethics Committee, however, found evidence that Ensign broke the Senate's rules in helping Hampton obtain lobbying work.

The ethics report said there is also evidence that:

Ensign and his parents "made false statements" about the $96,000 payment and that the money amounted to an unreported campaign contribution in violation of federal law and Senate rules.

Ensign discriminated on the basis of sex and engaged in improper conduct by terminating the Hamptons' employment because of the affair.

Ensign engaged in potential obstuction of justice and got rid of documents.

Boxer said the committee's special counsel found evidence that was "so disturbing" that if Ensign had not resigned the evidence "would have been substantial enough for consideration of expulsion."

She said the report on the Ensign scandal should be read by everyone and serve as a "cautionary tale" for all in public service.

"When you are in a position of trust and power, don't abuse it," Boxer said. "Don't misuse it because people could get hurt -- very, very hurt."

The ethics investigation of Ensign continued even after the Nevada Republican left the Senate on May 3. When Ensign announced he would step down, Boxer and Vice Chairman Johnny Isakson, R-Ga., issued a terse statement that he "made the appropriate decision" but vowed to keep on with the committee's work.

Republican Dean Heller was sworn in on Monday as Ensign's replacement.