Jace Crehan, 23-year-old man found guilty of the death of a convicted child molester faces a sentence for second-degree murder.
The man, from Louisiana, US, was found guilty on Thursday of the murder of Robert Noce Jr, a convicted child molester.
Noce died after being stabbed and strangled at home in the weeks following his sentencing to five years probation for pleading no contest to sexually molesting Britanny Monk.
Monk is Crehan's girlfriend.
Noce used to date Monk's mother and the allegedly molesting happened during that period, when Monk was aged 4 to 12.
According to The Advocate, Crehan killed Noce because he believed the judicial system had "failed" his girlfriend.
Monk has pleaded guilty to manslaughter for her role in helping break into Noce's trailer and attacking him. She was seven-months pregnant at the time, with Crehan's child.
Crehan told police he is "not sorry" for what he did.
The pair will be sentenced on January 18.
Crehan is facing life in prison while Monk could receive a sentence of up to 40 years in jail.