A jury convicted a Massachusetts man Thursday of raping and killing his 6-year-old cousin, rejecting his attorney's claim that the man was insane and "tortured by demons" when he committed the crime.

Ryan Bois, 22, received an automatic sentence of life in prison without the possibility of parole. The Norfolk Superior Court jury convicted him after eight hours of deliberation.

Prosecutors said Bois broke into his grandmother's house in Weymouth and raped and strangled Joanna Mullin, who was having a sleepover there in August 2007. He then wrapped the girl's body in a quilt and stole his grandmother's SUV.

Police found the girl's body inside the SUV after Bois led them on a high-speed chase, then crashed the vehicle into a taxi in Quincy.

Joanna Mullin's uncle, James Mullin, said he was grateful the jury saw Bois as "the manipulator and deceiver that he was."

"We're happy that justice was served," he said. "We'd rather have Joanna."

After the verdict was read, prosecutor Robert Nelson held his face in his hands and wept.

"This hits you, hits you in the heart," Nelson said outside the courthouse. "You try to hold it in and try to be professional in front of the jury. When the verdict came in, it hit me. I just lost it."

Bois' attorney, Beverly Cannone, argued her client was not responsible for killing his cousin because he was mentally ill. In her closing, she told the jury if they put aside their emotions, they'd see Bois wasn't a calculating killer.

In court Thursday, Cannone said Bois regretted what he did.

"He said he would trade places with Jo-Jo if he could," Cannone told the judge.

The prosecution argued Bois broke into the house to steal money, and when Joanna Mullin caught him, he killed the girl to cover it up.