"I strangled her and I've been stabbing her with various knives and whatnot," he added.
In October, Thompson was found dead aged 18 while in custody at a secure mental health facility - just four days before he was due to stand trial accused of murdering his mother.
STABBED 118 TIMES
The police officer who arrested Thompson at the home said the teenager was "extremely calm and composed" and "seemed to be more concerned about his cat".
On Monday, an inquest into the death of speech therapist Mrs Thompson heard that her son had been visiting her for the weekend, having recently moved to live with his father, who is a magician, in Barnsley, South Yorkshire.