CHARLOTTE, N.C. -- A registered sex offender has been charged with the brutal sexual assault of a woman who was at his home to take care of him.

Police said William Johnson, 55, attacked his caregiver at his home on Murdock Road, off The Plaza, in north Charlotte.

The victim said the assault happened several weeks ago, but she was too scared to come forward until now.

Neighbors said they only knew Johnson as the nice old man who used to ride his bike around the neighborhood.

"I just thought he was a regular guy moving into the neighborhood. You never saw anything weird or anything going on," said one neighbor.

According to the police search warrant, Johnson forced his caregiver into his home, tied her up and brutally sexually assaulted a woman. The warrant said Johnson then poured boiling water from a tea kettle over the victim's genitals.

Police said Johnson is a convicted sex offender who served less than 15 years of a 40-year prison sentence for a rape in 1988.

"It's real scary -- especially with kids around. I have my grandkids here on the weekends sometimes," said neighbor Cynthia Williamson.

Last year, Johnson was arrested for failing to register as a sex offender.