David Matusiewicz entered the plea Tuesday before a federal magistrate. He waived a hearing on a prosecution motion to detain him pending trial, and the judge ordered that he remain in custody.
Matusiewicz, his mother and his sister are charged with conspiring over several years to torment and stalk his ex-wife, Christine Belford, following a bitter divorce and custody battle. Belford and a friend were shot to death by Matusiewicz's father, Thomas, in February at the New Castle County courthouse before he turned the gun on himself.
Matusiewicz's mother and sister were arrested in Texas and are being returned to Delaware later this month.
