Three high school girls and their parents were found dead Saturday morning at their home in eastern Iowa, and the couple's son was arrested in Illinois and considered a suspect, officials said.

The victims were found shot at about 4 a.m. near Bonaparte, according to the Van Buren County sheriff's office. It was not immediately clear what prompted the slayings.

Shawn Bentler, 22, was arrested Saturday in Quincy, Ill., on an unrelated charge of possession of drug paraphernalia, the Van Buren County sheriff's office said. The Iowa Department of Public Safety said he is a suspect in the slayings.

Quincy is about 57 miles southeast of the family's home.

Parents Michael Bentler, 53, and Sandra Bentler, 47, were found dead with their daughters Sheena Bentler, 17, Shelby Bentler, 15, and Shayne Bentler, 14, Van Buren County authorities said.

The Harmony school district confirmed three of its female high school students — a freshman, sophomore and senior — and their parents were killed.

The slayings shocked residents of this eastern Iowa town, located about 145 miles southeast of Des Moines.

"The whole town knew the family," resident Marilyn Thomas said. "This is only a town of 465 people."

School officials said they will have counselors available Monday to speak with grieving students.