William Jaggs, a 23-year-old Oxford University student and prolific cannabis user, stabbed fashion designer Lucy Braham 66 times at her home near Harrow, the public school in North-West London.
The paranoid schizophrenic was found covered in blood beside Lucy's body, having plunged the knife into his own chest last September.
The former Harrow pupil, whose father is a teacher at the school, started using drugs when he was 14, moving on from cannabis to cocaine.
He was sent to Broadmoor secure hospital this month for an unlimited period after admitting manslaughter on the grounds of diminished responsibility.
