July 28, 2012 -- The New Hampshire hospital lab technician indicted last week for infecting 31 people with Hepatitis C might have infected "tens of thousands" of patients in at least 13 hospitals, ABC News has learned.

David Kwiatkowski, a former lab technician at Exeter Hospital in New Hampshire, had allegedly been stealing syringes of the anesthetic Fentanyl intended for patients, injecting his own arm and then refilling those empty syringes with another liquid-like saline, according to a statement from the United States Attorney's Office in New Hampshire.

Since Kwiatkowski tested positive for Hepatitis C in June 2010, he passed it on to the hospital patients who were injected with his used, saline-filled syringes, according to the affidavit.

"If he knew that he was infected and he put those needles back on the shelf, that is the definition of evil," Dr. Richard Besser, ABC News' Chief Health and Medical Editor, told Good Morning America. "Anyone who was in those hospitals when he was working there is potentially at risk. We're talking tens of thousands of people."

Kwiatskowski, 32, was a temporary employee at Exeter Hospital who has worked in at least eight hospitals in 13 states, Besser said.

Exeter Hospital issued a press release this week, indicating that the state Department of Health and Human Services and its Division of Public Health Services have decided to expand Hepatitis C testing to anyone who was a patient in one of the hospital operating rooms or the intensive care unit. Government health officials are urging about 6,000 patients to get tested in Exeter Hospital alone, according to the release.

"You go under and you wake up hours later and you don't know who was around you," a former patient told The Boston Herald on condition of anonymity this week. "I'm scared. I have no idea who was around me when I was under and unfortunately, I was there three different times."

Kwiatkowski was arrested and indicted on July 19 for allegedly acquiring a controlled substance by fraud and tampering with a consumer product with "reckless disregard" for the risk of others, according to an affidavit filed in U.S. District Court for the District of New Hampshire.

"The evidence gathered to date points irrefutably to Kwiatkowski as the source of the Hepatitis C outbreak at Exeter Hospital," U.S. attorney John P. Kacavas said in a press release. "With his arrest, we have eliminated the 'serial infector' posed to public and health safety."

But Marlborough Police actually picked Kwiatkowski up at a Massachusetts Holiday Inn nearly a week before his arrest, on a July 13 medical call, according to police narrative obtained by ABCNews.com. After finding Kwiatkowski intoxicated and surrounded by pills and a note, officers determined he was "trying to harm himself."

"I noticed he was very unsteady on his feet and had a strong odor of alcohol coming from his breath," Officer James O'Malley wrote in the report.

O'Malley said he noticed pills strewn about the floor and on a glass table. He also found what appeared to be a suicide note signed by Kwiatkowski.

"Please call [redacted] and let her know I've passed away," it said. "Tell her I couldn't handle this stress anymore."

Officers took six medication bottles from the room and transported Kwiatkowski to a nearby hospital, where he was arrested a week later.

Exeter Hospital employees discovered the outbreak in May 2012, prompting an investigation that spanned several local, state and federal government agencies, including the FBI, according to court documents obtained by ABCNews.com.

Investigators wrote that they suspect Kwiatkowski grabbed the loaded Fentanyl syringes when he brought lead aprons into the procedure room, into an area he didn't need to be inside at all. They suspect Kwiatkowski then replaced the syringes of Fentanyl, which is more powerful than morphine, with saline syringes that were tainted with his strain of Hepatitis C.

Kwiatkowski was known for erratic behavior and suspected of abusing controlled substances, according to the affidavit. Other hospital employees said he would often sweat through his scrubs and made frequent trips to the bathroom.

One employee told investigators she saw "fresh track marks" when she tried to draw his blood. Another told investigators he remembered seeing Kwiatkowski with "a red face, red eyes and white foam around his mouth" during a shift at the lab.

Kwiatkowski also had a tendency to lie, employees told investigators. He told coworkers that he played baseball in college, and that his one-time fiancée died "under tragic circumstances," neither of which were true. He also once excused bloodshot eyes by saying he was crying all night about a dead aunt who never existed.

When his roommate inquired about the needles in his laundry, Kwiatkowski told her he had cancer and was being treated at Portsmouth Regional hospital, according to the affidavit. Investigators found no documentation to prove this.

In 2008, Kwiatkowski was fired from his contract job at the University of Pittsburgh Medical Center after he was found in an area to which he was not assigned, the New Hampshire Union Leader reported Friday. Two years later, he was fired again, this time from his job as a radiation technician at Arizona Heart Hospital in Phoenix after he was discovered unconscious in a locker room, with syringes and needles on his body, according to the Union Leader.

Kwiatkowski was arrested on July 19 in Massachusetts, where he was being treated at a hospital. He faces up to 24 years in prison. Each offense could also result in a $250,000 fine.

ABCNews.com reached out to Kwiatkowski's lawyer this morning, but he was unavailable for comment.