For five years, the authorities say, a woman named Shannon worked at about 20 nursing homes and rehabilitation centers across at least four states, tending to patients.

Sometimes she used the last name Parham, other times Armstrong and, on occasion, Grimes. But according to law enforcement officials, one thing was constant: She didn’t have the qualifications or credentials to work as a nurse.

This week, as part of its continuing investigation, the Pennsylvania State Police charged the woman with endangering the welfare of care, unlawful use of a computer, identity theft, forgery, theft by unlawful taking and several other charges, the agency said in a news release on Wednesday.

Now, the state police is asking health care companies across Pennsylvania to help investigators retrace where she worked and under which aliases among at least 20 that the authorities said she was known to have used.

The police charged the woman as Shannon Nicole Womack, the name she eventually gave after her arrest on April 5. The Pennsylvania driver’s license she handed to a state trooper after being pulled over identified her as Shannon Nicole Lawson, 39.

Fingerprinting added to the puzzle. According to court records, running her prints through a computer system yielded yet another name: Shannon Nicole Robinson.