LANCASTER, Pa. -

A man convicted of robbing and assaulting three elderly Mennonite sisters in Lancaster County has been sentenced to 12 to 40 years in prison.

The sentencing judge said Dereck Taylor Holt is a danger to the community. Holt, 22, will undergo psychiatric treatment in prison.

Holt pretended to be an insurance salesman to get inside the Clay Township home in December, then bound the 85- to 91-year-old victims, hit them with a stun gun, sprayed their home with household chemicals and left them for dead, authorities said.

Mennonites share a common heritage with the Amish but are generally more assimilated into mainstream culture than the Amish, who shun modern life.

Investigators initially believed the sisters were targeted because of their religion, but charges of ethnic intimidation were dropped.