Sebastian Van Stockum — the Connecticut man accused of killing his mom — once took a high school Forensic class that had the trappings of a Jeffrey Dahmer crime scene with simulated blood spatter, dead bodies, and human skeletons, according to a former classmate.

The ex-classmate tells TMZ she was in the same Forensics class with Stockum back at New Canaan High — where the lessons included blood-spatter experiments in which students would stand on tables with a ruler and squirt fake blood to study blood patterns.

Students also learned how to zero in on someone’s time of death based on body temperature, as well as studying skeletons and bones, and even watching a documentary about human corpses. Other projects included breaking down fabric under a microscope, learning about DNA, and solving mock crime scenes.

As we reported … Sebastian was busted Friday after cops got a call from someone claiming he’d killed his mom.