Students Barnaby Webber and Grace O'Malley-Kumar, both 19, and school caretaker Ian Coates, 65, died after being attacked on 13 June.
Valdo Calocane denied murder but admitted manslaughter in November.
His pleas of not guilty to murder and guilty to manslaughter were accepted at Nottingham Crown Court.
They were accepted on the basis of diminished responsibility due to "serious" mental illness, the hearing was told.
Nottingham attacks: Court accepts triple killer’s guilty plea
Btw the guy who done it is a nig nog
Valdo Calocane denied murder but admitted manslaughter in November.
His pleas of not guilty to murder and guilty to manslaughter were accepted at Nottingham Crown Court.
They were accepted on the basis of diminished responsibility due to "serious" mental illness, the hearing was told.
Nottingham attacks: Court accepts triple killer’s guilty plea
Btw the guy who done it is a nig nog