If it was James Bell, Sheila's biological mother, or a hit man team, as Mike suggested, it will be a 'first ever' situation.
An innocent man (Jeremy) being framed. But not framed by the killer/s. Framed by people who didn't commit the crime (relatives, Julie). Assisted by the police/experts changing stance to create an industrial frame.
If AP or AE committed the massacre, as suggested by Mike/Sherlock, this is more straight forward. The murderers were trying to frame another person - Jeremy. Again assisted by the police/experts changing stance.