BOONE, Iowa — A body found in a river is believed to be a 15-year-old Iowa girl who was kidnapped by a registered sex offender while she and a friend were walking home from school, authorities said early Saturday.

High school freshman Kathlynn Shepard has been missing since May 20, when she and a 12-year-old were lured into a pickup truck that police believe was driven by Michael J. Klunder. The younger girl was able to escape after he took them to a hog confinement facility.

Gerard Meyers, assistant director of field operators of the Iowa Division of Criminal Investigation, said fisherman found the body Friday night in the Des Moines River near Boone, concealed by debris.

Boone County sheriff’s deputies then recovered the body. An autopsy was scheduled for Saturday morning.

“We’re fairly confident the unfortunate circumstance this evening was the recovery of Kathlynn,” Meyers said at a news conference in Boone.

Hundreds of officers and volunteers had searched for Kathlynn, but hopes of finding her alive were dampened when testing confirmed that blood found on Klunder’s truck and at the hog building was Kathlynn’s.

The girls had just stepped off their school bus and were near their homes in Dayton, a small town about 60 miles north of Des Moines, when Klunder asked whether they wanted to make money mowing lawns, police said. He promised he would take them for a ride to ask their parents, but instead drove them several miles away to a hog confinement building where he worked.