NEW HAVEN, Conn (Reuters) - A judge formally sentenced Joshua Komisarjevsky to death for the murders of a mother and her two daughters during a brutal home invasion in Connecticut, saying he committed a crime of "unimaginable horror."

Judge Jon Blue on Friday told Komisarjevsky, 31, that he alone was to blame for his new address on death row after the 2007 triple murders of Jennifer Hawke-Petit, 48, and her daughters Hayley Petit, 17, and Michaela Petit, 11, and beating of husband and father Dr. William Petit Jr.

"This is a terrible sentence but one you have written for yourself," Blue told Komisarjevsky in New Haven Superior Court.

"Your crime was one of unimaginable horror and sadness," the judge said. "Your fate is now in the hands of others. May God have mercy on your soul."

He set an execution date of July 20, 2012, pending an appeal, which could drag out the matter for years.

Before the judge spoke, Komisarjevsky, dressed in an orange jumpsuit, denied he killed or raped anyone.

But he told the judge, "The clock is now ticking and I owe a debt I cannot repay."

Komisarjevsky now joins his accomplice, Steven Hayes, 48, who was sentenced to death last year for killings in which Hawke-Petit was strangled and the girls died of smoke inhalation after the home was set afire. Hawke-Petit was raped and Michaela Petit was sexually assaulted.

The killer's portrayal of innocence was in stark contrast to the "evil" described by the sole survivor of the attack, Dr. Petit, who told the court how Komisarjevsky's actions had destroyed his family.

"July 23, 2007 was my own personal holocaust," said Petit, who was beaten unconscious but escaped. "Evil does live among us."

He said he missed his late night chats with his wife and their partnership raising their daughters, who he will never walk down the wedding aisle and who will never bear the grandchildren he would have loved to have known.

Outside the courthouse, Petit's father spoke of the slow emotional recovery of his son, who is now engaged to be married.

"He's starting to come back a little bit now to what he was. He never will come all the way back," William Petit Sr. told reporters after the sentencing.

"To know Bill, the brilliant young doctor that he was, the happy young man, the good father, brother, cousin, uncle, all of those things, and son, and then to see him after this is just heartbreaking."

A jury convicted Komisarjevsky last fall, then sentenced him to death.

Komisarjevsky targeted Hawke-Petit and her younger daughter at a local grocery store and followed them home, he confessed during the investigation. He later returned with Hayes in the early morning, while the family was sleeping, and bashed Petit with a baseball bat and tied him to a pole in the basement.

After ransacking the home for valuables and finding little, they two men tied the girls to their beds and concocted a plan to take Hawke-Petit to the bank to withdraw $15,000.

Despite his last-minute denial at the sentencing, Komisarjevsky admitted to investigators that he molested Michaela while her mother was at the bank, according to police.

With the police circling the home, Hayes raped and strangled Hawke-Petit and the two men doused the family room and the girls' beds with gasoline.

Dr. Petit escaped through bulkhead doors in the basement as the home went up in flames.

Police caught Komisarjevsky and Hayes as they tried to flee.

During the trial, prosecutors laid blame for the predatory nature of the crime and the escalating violence on Komisarjevsky.

Defense attorneys said Komisarjevsky never intended for anyone to die and suffered mental health problems stemming from his upbringing by rigidly religious parents as well as from suffering several concussions and years of childhood sexual assault at the hands of a foster child in the family home.

Komisarjevsky's sentencing brings to 11 the number of men on the Connecticut's death row, according to the Death Penalty Information Center.

Connecticut has executed only one person, in 2005, since the death penalty was reinstated in the United States in 1976, the center said.

(Editing by Ellen Wulfhorst, Barbara Goldberg and Paul Thomasch)