NEW HAVEN, Conn — The trial of a Connecticut man charged with killing a woman and her two daughters during a gruesome home invasion opened today with a defense attorney telling the jury that the evidence will “shake your confidence in humanity” but blaming his co-defendant for the slayings.

Joshua Komisarjevsky, 31, faces a possible death sentence if convicted. His co-defendant, Steven Hayes, was sentenced to death last year.

Komisarjevsky did not intend to kill the three, said his attorney, Walter Bansley.

Authorities say Komisarjevsky and Hayes, two paroled burglars, broke into a Cheshire home in July 2007, beat William Petit and tied up his wife, Jennifer Hawke-Petit, formerly of Slippery Rock, and the couple’s daughters, 11-year-old Michaela and 17-year-old Hayley. Hayes forced Hawke-Petit to withdraw money from a bank before he raped and strangled her in the family’s home.

The girls, who had pillowcases placed over their heads, died of smoke inhalation after the house was doused with gasoline and set on fire.

Petit also was tied up but managed to escape to a neighbor’s house to get help.

“The evidence you are about to hear will shake your confidence in humanity,” Bansley said. “The deaths that occurred were senseless, unnecessary and tragic.”

Bansley portrayed Komisarjevsky as panicked and indecisive, claiming he suffers from “cognitive difficulties” that makes him unable to make quick decisions in stressful situations.

During Hayes’ trial, the defense blamed Komisarjevsky for escalating the violence and portrayed Komisarjevsky as the mastermind of the crime. They said Komisarjevsky had a long history of residential break-ins, attacked Petit with a bat, molested Michaela and pressured Hayes to sexually assault Hawke-Petit.

Prosecutors have repeatedly said both men were equally responsible for the crime.