University of Idaho killer Bryan Kohberger's sister Amanda could have been called as a witness for the prosecution if his case went to trial, according to a report. Kohberger, 30, accepted a deal to plead guilty to the murders of four students - Kaylee Goncalves, Madison Mogen, Xana Kernodle and Ethan Chapin - just days after prosecutors listed his sister as a potential trial witness, reported TMZ on Tuesday, October 14, citing newly unsealed court documents. Amanda was Kohberger's only immediate family member listed in the documents, per TMZ.