NASHUA, N.H. – A man who admitted he took part in a deadly machete and knife attack on a New Hampshire woman and her daughter was convicted of murder Friday after jurors rejected his claim of insanity.

Minutes after the jury returned the verdict against 21-year-old Christopher Gribble, Superior Court Judge Gillian Abramson imposed the mandatory sentence of life without parole, telling Gribble, “Infinity is not enough jail time.”

For the first time in the proceedings, victim Jaimie Cates, now 12, appeared in the courtroom. She witnessed the sentencing.

Most of Gribble’s knife blows targeted the girl. A lead investigator said that even as she lay on the bedroom floor bloodied and feigning death, she opened one eye and watched as Gribble plunged a knife into her mother’s throat.

Jaimie entered the courtroom after her father had delivered an emotional victim-impact statement in which he said he felt it was his “duty as a husband and a father to be here for every moment of this trial.”

“I’ve lived the accounts of Kim’s murder one excruciating blow after another,” David Cates said. “Through these accounts I have heard my wife’s last breath, heard my daughter’s screams, seen my daughter’s perfect body mutilated.”

Gribble remained as impassive as he was had when the verdicts were returned and when he testified in detail about the attacks.

“I don’t have any illusions this invasion of the sanctity of our home will ever be behind us,” David Cates said. “Jaimie and I won’t live a day without thinking of the horrific things that happened in our home and that Kim will never again be with us.”

In an unusual move, the jurors returned to the jury box to witness the sentencing. Some glared at Gribble; others smiled.

Gribble was given the opportunity to speak before sentencing but declined.

When he appeared in court for the verdict, Gribble wore slacks and a dress shirt. When he reappeared in court for his sentencing moments later, he was wearing bright orange prison garb and shackled at the wrists.

Abramson thanked Jaimie for her presence in the courtroom and assured her that the men involved in this “horrible crime” could never hurt her again.

Jaimie left the courtroom through a door to the right of the judge’s bench, dodging media.

Defense attorney Matt Hill declined to comment.

The verdict and sentencing punctuated one of the most brutal crimes in recent state history. Steven Spader, of Brookline, who wielded the machete in the attacks, was convicted and sentenced to life without possibility of parole.

New Hampshire State Police Lt. James Geraghty said after the proceedings he was glad investigators were able to take Gribble and Spader into custody the day after the home invasion.

“I think they would have done it again,” Geraghty said. “Another tragedy was right around the corner.”

Lead prosecutor Jeffery Strelzin said Gribble’s multiple life sentences were the maximum allowed by law, but “far less than what he deserves.”

“For someone to leave home to provide for their family and learn complete strangers have come in and slaughtered their family is incomprehensible,” Strelzin said of the crimes.

The jury deliberated approximately two hours before finding Gribble guilty of two counts of first-degree murder, attempted murder, conspiracy to commit murder, conspiracy to commit burglary and witness tampering.

Gribble admitted he took part in the Oct. 4, 2009, home invasion and that he and Spader intended to kill anyone they found in the house.

Gribble took the stand in his own defense during the 11-day trial, claiming he had been abused by his mother and that he had fantasized about torturing and killing her. He asked a jury to find him not guilty by reason of insanity. Prosecution experts who examined him testified that he had an anti-social personality but was not insane.