The District Court presided over by Mr Ebenezer Kweku Ansah said after listening to prosecution, that the two accused ought to explain how they came by the grenades from Russian Federation.
Judy Malinowski surfaced until she died last June, expecting that the recording could be played at her boyfriend trial.
Robert Bever pleaded guilty in 2016 and was sentenced to life in prison without parole.
And on Friday Franklin County Judge Guy Reece allowed the footage saying officials knew of no other case in which a victim would testify at his or her own murder trial.
His attorneys tried to block it by citing a legal technicality, claiming it was improperly obtained by prosecutors.
Ms Malinowski, 33, sustained burns to 80pc of her body, and was bed-ridden in hospital for the two years after her attack, where she eventually died. "I think it's the first step toward what her legacy should and will be".
The judge allowed it on the grounds that it is an unprecedented case where the victim is able to give evidence after their own death.
Slager has always maintained that he set her on fire by accident when he lit a cigarette. He just stood there and did nothing. He had run up from behind to cover her in gasoline.
Judy Malinowski and her two children.
However, once Malinowski died, a grand jury charged Slager on charges of murder and aggravated murder.
Malinowski inspired OH legislation requiring six additional years in prison for crimes that permanently maim or disfigure victims.
Slager is shown above in a recent court hearing.
She dropped her ears along with 2 palms at the strike, as Fox News previously reported, also has been left with deep wounds on her back and buttocks.
She underwent a total of 56 surgeries in that two year period. Doctors wanted to perform on her but she was too weak to withstand another procedure. He is due in Tulsa district court on Monday.
Malinowski's ex-boyfriend, Michael Slager, was sentenced to 11 years in prison after pleading no contest in 20-16 to charges including felonious assault and aggravated arson.
Now, given the more serious charge, he faces life imprisonment.