05/04/2011 at 03:15 PM EDT
Phoebe Prince's mother tearfully lashed out in a Massachusetts court Wednesday at the teenagers who bullied
her daughter before the 15-year-old girl committed suicide.
Anne O'Brien singled out Sean Mulveyhill, who briefly dated Prince, claiming he was in a "predatory" relationship with the girl before encouraging other teens to torment her.
"There is a dead weight that now sits permanently on my chest," O'Brien said at the sentencing in the Northampton courtroom of two of the six teens charged in connection with Prince's case.
In a deal with prosecutors, Mulveyhill, 18, pleaded guilty to misdemeanor criminal harassment and was sentenced instead to one-year probation and community service.
His ex-girlfriend, Kayla Narey, 18, who reached a similar plea deal, apologized, breaking down in tears as she said, "I was the weak one and that behavior will always be with me. I’m sorry, Phoebe. I am sorry about the unkind things I said, I'm sorry I laughed when someone was shouting things at you."
"I am immensely ashamed of myself," added Narey. "I am sorry for my role in this tragedy and I am deeply sorry for what my behavior has caused my family, my loving friends and the South Hadley community."