An internal Massachusetts State Police investigation has cleared agency officials of wrongdoing for hiring a trooper with a drug-dealing past, and blamed her for not disclosing her role as a key witness in a high-profile trafficking case.

Trooper Leigha Genduso resigned Friday afternoon upon reviewing the internal investigation, which her attorney called “a coverup from day one.’’ She received a dishonorable discharge, which she said she will appeal.

The internal affairs report recommended her termination and cited 11 violations of the agency’s rules and regulations. It concluded a 2013 background check was “thorough and complete’’ and the only reason the investigation didn’t turn up her “illicit past’’ was because of Genduso’s “omissions and deceptive responses.’’