(CNN) -- A report by the Massachusetts inspector general released Tuesday said that former drug lab technician Annie Dookhan was the "sole bad actor" at a Boston drug lab once responsible for tests related to thousands of criminal cases, and that directors of the facility were "ill-suited" to oversee her and other lab technicians.
The state of Massachusetts says Dookhan doctored evidence to change test results at the Hinton State Drug Laboratory. After Dookhan's co-workers told state police her work might be unreliable, the state attorney general's office began investigating the case in July 2012. The tampering called into question at least 40,000 cases going back to 2003 and, in some cases, may have wrongfully convicted the innocent.
She was found guilty of multiple charges related to the case, including obstruction of justice, mishandling of drug evidence and lying about holding a master's degree in chemistry from the University of Massachusetts. She was sentenced in November of last year to three to five years in prison.
"Dookhan was the sole bad actor at the Drug Lab. Though many of the chemists worked alongside Dookhan for years, the OIG (Office of the Inspector General) found no evidence that any other chemist at the Drug Lab committed any malfeasance with respect to testing evidence or knowingly aided Dookhan in committing her malfeasance," the report said.
But the report didn't stop short of blaming the unprecedented breach in confidence solely on Dookhan.
"The directors were ill-suited to oversee a forensic drug lab, provided almost no supervision, were habitually unresponsive to chemists' complaints and suspicions, and severely downplayed Dookhan's major breach in chain-of-custody protocol upon discovering it," according to the inspector general's report.
The Inspector General's Office reviewed more than 200,000 documents -- including e-mails, lab results and lab records -- and interviewed more than 40 people who worked with the drug lab to check for deficiencies, the report said.
An investigation by Inspector General Glenn Cunha and his office showed that former Department of Public Health Commissioner "John Auerbach and his staff failed to respond appropriately to the report of Dookhan's breach of protocol" and "the investigation DPH conducted was far too narrow," the report said.
Gov. Deval Patrick closed the lab, in Boston's Jamaica Plain neighborhood, in August 2012. That year, Auerbach submitted his letter of resignation from the Public Health Department to Patrick amid the investigation, and the Massachusetts State Police now oversee all of the state's drug cases.
The Inspector General's Office concluded that "all samples in which Dookhan was the primary chemist should be treated as suspect and be subject to careful review."
In addition to the drug samples Dookhan mishandled, an additional 2,000 drug samples not handled by Dookhan were found to potentially contain "exculpatory evidence" to defendants in criminal cases because the drug lab failed to disclose "additional, inconsistent testing results," the report said.
The Inspector General's Office says it is retesting these samples and will give prosecutors and defendants accurate information about the tests when they're completed.
In November 2012, Donta Hood, who was convicted of a cocaine charge in 2009, was released from prison after his defense team questioned the validity of Dookhan's testing results and her expert testimony.
After his release, he was arrested on a gun possession charge. While on bail for that charge, he was arrested and charged with the murder of Charles Evans, 45, the Brockton Police Department said.
Hood is awaiting trial on the murder charge. The next hearing in this case is a motions hearing on March 11, the Brockton Superior Court Criminal Clerk's Office said.