Kimberly Cates Update: Murder Co-Defendant Admits Killing N.H. Mother, Pleads Insanity

NASHUA, N.H. (CBS/AP) A 21-year-old man admitted in court Monday that he hacked 42-year-old Kimberly Cates to death and seriously wounded her 11-year-old daughter, Jaimie, during a 2009 home invasion. However, Christopher Gribble claimed he was insane when he did it.

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

Gribble waived his right to a jury trial. The burden now shifts to his lawyers to prove he was insane during the Mont Vernon home invasion.

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.

Prosecutors say Spader wielded a machete and Gribble a knife in the Oct. 2009 attacks on the mother and daughter.

Gribble opted for a jury trial on the insanity claim. Jury selection is scheduled to begin Feb. 10.

Gribble's lawyers will also attempt to suppress a detailed confession he gave to investigators the day after the crime. They claim investigators improperly told Gribble they were

offering him "a lifeline" if he talked with him and strongly implied that he would drown under the wave of evidence if he did not cooperate.

Even though Gribble has admitted to the crimes, prosecutors are fighting the suppression motion. Gribble's tape-recorded confession is expected to show how composed he was as he detailed the crimes.

COMPLETE COVERAGE OF THE KIMBERLY CATES MURDER ON CRIMESIDER