Willson was arraigned Monday on one count each of murder and felony firearm possession.
Magistrate Mark Blumer denied bond for Willson, who has been in police custody since Friday.
Andrew Willson called police shortly before 7 a.m. Friday and lied that he came home from a drive to find his mother had been murdered, an Ingham County (Mich.) Sheriff's detective told the judge in a hearing that led to charges against the teen.
Lisa Marie Willson, 51, was found dead in a bedroom of her home near Williamston, Mich., in Wheatfield Township, police said. She was shot once in the back of the head.
Investigators determined that no one besides her and her son had been inside the house the night of the killing, Detective Charles Buckland testified.
Andrew Willson talked to his mother about the puppy Thursday evening, and she told him he would have to take the dog to his father's home, Buckland testified.
The teen told detectives that in the overnight hours he removed a .22 Magnum rifle from a locked cabinet, then went into his mother's room and shot her in the back of the head as she slept, Buckland said.
He then drove around back roads for a while before discarding the rifle. Police recovered the weapon, which had a spent shell casing and a live round in it.
Source: USA Today