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.