Calling the case chilling and troubling, authorities announced an indictment Thursday against a convicted sex offender whom they say videotaped himself sexually assaulting children from his wife's unlicensed day care business.

Prosecutors said John Burbine's wife told parents he was an experienced baby sitter. But instead, authorities allege that the 49-year-old Wakefield man preyed on 13 day care clients ranging from 8 days to 3 1/2 years old, with many of the assaults happening in the victims' homes.

Middlesex District Attorney Gerard Leone said Burbine has been in custody since September on charges involving one victim that grew out of an abuse complaint from July. Burbine faces an indictment including 100 criminal counts.

"I have never seen a case this bad," Leone said Thursday.

The prosecutor said the abuse occurred between August 2010 and August 2012. Leone said the children lived in the Boston suburbs of Stoneham, Medford, Newton, Reading, Melrose, Woburn and Waltham. He said there may be more victims that investigators haven't identified.

The prosecutor said Burbine's wife, Marian Burbine, operated Waterfall Education Center in Wakefield. The business advertised services including short- and long-term child care, group child care, overnight newborn care and summer camp alternative care.

Leone said investigators believe Marian Burbine didn't know her husband was sexually abusing children, but she knew he was a convicted sex offender and that state officials believed child abuse allegations against him in 2005 and 2009 that never led to prosecution. Both spouses face charges of operating an unlicensed day care business.

Heather Johnson, a spokeswoman for the state Department of Early Education and Care, said Thursday that the Burbines never applied for a day care license and never got one.

Leone said investigators began a probe after previous abuse complaints that didn't lead to criminal charges. This summer, authorities got a cease and desist order for Waterfall Education Center because it wasn't licensed. That led to search warrants for the Burbines' business and home that Leone said led investigators to seize video evidence of the child abuse.

Among the offenses John Burbine faces are 40 counts of aggravated forcible rape of a child. His attorney, William Barabino, said Thursday that the defendant will plead not guilty at his Dec. 12. arraignment. A judge previously ordered the defendant held without bail.

Marian Burbine is free on $1,000 bail following her Oct. 1 arraignment in Middlesex Superior Court. She must wear a GPS monitoring device as a condition of her bail. An indictment against the 46-year-old includes six counts of reckless endangerment of a child. Her attorney didn't immediately return a message Thursday seeking comment.

Leone said John Burbine is a Level 1 sex offender, following a 1989 conviction for indecent assault and battery.

Barabino said he hasn't seen evidence prosecutors say they seized from Burbine's computer, including videos.

"Everything they say exists was found on a computer," Barabino said. "He's been cooperative in the process with the district attorney to more than a reasonable degree, and we'll wait for the evidence."

Barabino said Burbine grew up in Wakefield, where his father was a police officer. He said John and Marian Burbine have been married for nearly 20 years. The couple does not have children. Burbine has a master's degree in management from Lesley University in Cambridge, Barabino said.

The lawyer also said his client had worked at a sporting goods store in Reading and as an adjunct professor at North Shore Community College in Danvers teaching an introductory computer class.

College spokeswoman Linda Brantley said the school fired Burbine following his arrest.