Authorities say 22-year-old Gary Charles Gerlach was arrested at a Wildwood, N.J. hotel on Sunday, two days after the bodies of 22-year-old Makenzie Hess and her mother, Mona, were found at a home in Lancaster County.
A police affidavit says Gerlach confessed to the killings and shared specific details about the scene with detectives.
District Attorney Craig Stedman says Gerlach had been living in the family's Upper Leacock Township home.
An autopsy is set for Monday.
Gerlach remains jailed in New Jersey. Online court records don't list an attorney for him.