Nursing homes in several states have been targeted by a group of male thieves who sneak into to long-term care facilities dressed as female nurses.

Nursing homes in the Denver area have been hit most recently, with at least 20 separate incidents, the Denver Post reported. Local authorities said the thieves wait until residents are away from their rooms for meals or other activities and then steal credit cards. Investigators say the cards are usually used at retailers such as Wal-Mart and Kmart, with estimated fraudulent expenditures already between $50,000 and $100,000.

Colorado authorities arrested a long-haired, 28-year-old man dressed in scrubs last week in connection with at least some of the crimes. Currently out on bond, he was convicted of similar offenses five years ago in Louisiana, they said. Law officials said they believe the cases are linked to a national crime ring that has executed similar burglaries, starting in April, in Louisiana, Georgia, Texas, Kansas and Alabama, the newspaper reported.