A 21-year-old man admitted in court Monday that he hacked a mother to death and seriously wounded her young daughter during a 2009 home invasion but said he was insane when he did it.

Christopher Gribble of Brookline waived his right to a jury trial on whether he killed 42-year-old Kimberly Cates and seriously wounded her 11-year-old daughter, Jaimie.

The burden now shifts to Gribble's lawyers to prove he was insane during the Mont Vernon home invasion.

If the jury finds he was sane at the time, Gribble will be sentenced to life in prison without the possibility of parole.

If jurors find him not guilty by reason of insanity, Superior Court Judge Gillian Abramson would hold a hearing on whether he is a danger to society. If she finds that he is a danger, she will commit him to the secure psychiatric unit of the New Hampshire State Prison. He would then be entitled to have a review of his threat to society every five years.

Gribble answered, "Yes, your honor" when asked if he committed murder, attempted murder, conspiracy to commit murder and burglary, and tampered with a witness. He then pleaded not guilty by reason of insanity to each charge.

Gribble listened intently as Senior Assistant Attorney General Jeffery Strelzin detailed the evidence the state was prepared to present. It mirrored the evidence that was presented to the jury that convicted 19-year-old Steven Spader of first-degree murder last month.