A New Hampshire teenager convicted in the killing of a disabled Wal-Mart cashier was sentenced Thursday to 20 to 40 years in prison, capping the prosecutions of four young people who set out to avenge the victim's passes at a co-worker.

Michael Robie, 19, was the last of the four to be sentenced for the murder of Christopher Gray, 25, of Groton, Vt., who was lured to a girl's home on the pretext of watching movies and then stabbed more than 30 times as he stood by a bonfire.

Robie, who was in jail on unrelated charges at the time, didn't participate in the stabbing but plotted it beforehand with girlfriend Amber Talbot and the other two, their conversations captured on tape-recorded telephone calls from Robie's jail cell.

"You called the shots from the jail," said Gray's aunt, Shirley Kingsbury, sobbing as she berated Robie in court Thursday. "You could've stopped this violent crime at any time, and you deliberately chose not to. You let them do your dirty work."

The plot took shape after Talbot — who worked in the Wal-Mart in nearby Woodsville — told Robie that Gray had been making passes at her at work, following her around and telling her she was cute. Gray, who had a speech impediment and low IQ and was considered developmentally disabled, also told suspect Timothy Smith he liked her and described what he would like to do with her.

On Oct. 6, 2008, Talbot invited Gray to watch movies at her home. Once there, Smith, 24, and cousin Anthony Howe, 19, stabbed and strangled Gray as they stood around a bonfire. All three pleaded guilty to conspiracy and second-degree murder; Smith and Howe got 40 years to life, Talbot 25 to 50 years.

Robie, who was originally charged with conspiracy to commit murder, later pleaded guilty to lesser charges — assault, assault conspiracy, hindering apprehension and conspiracy to hinder apprehension — after prosecutors acknowledged that he never explicitly ordered the killing.

His lawyer, James Moir, told the judge Thursday that Robie had been wrongly characterized as the mastermind of the killing. He said in some of the conversations, Robie was heard telling Talbot to go the police or get a restraining order against Gray if he was bothering her so much.

Prosecutor Jeffery Strelzin said that was true, but that given the overall context of 200 hours of recorded conversations, it was clear Robie wanted Gray harmed at least, if not killed.

"In fairness, there were times that the defendant said Amber should go and talk to people. At the same time, those statements were always interspersed with statements like `I'll kill him myself when I get out,' `I want him gone,' `He's never going to be around any more.' In the full context, it's clear that the defendant wanted Chris Gray harmed," Strelzin said.