Dr. Frankenstein combines parts from stolen corpses, including the brain of a criminal and brings the monster to life with electricity from lightning. Terms like insane and crazy appear in conversation repeatedly throughout the film, sometimes referring to Dr. Frankenstein himself (0:19).
At a medical lecture the professor shows his audience how to distinguish a normal brain from that of a criminal by its external appearance. (0:07)
We see the monster raving in his cell (0:36).
In order to control the monster the two doctors inject him with a "very strong half grain solution" of a central nervous system depressant, probably a barbiturate (0:37). The professor notes that to maintain the effect he must inject larger doses more frequently, evidence of developing tolerance (0:42).
The monster, as though continuing to mimic her game of throwing flowers into the water, throws Maria into the water (0:50). After she disappears and drowns he appears unhappy, and there is no evidence that he intended to harm her or even that he anticipated the consequences of his action, which her father calls murder. Might he pass the wild beast test to mount a successful insanity defense? Would the fact that he has killed twice before make a difference?
Maria's father brings her body into town (0:55).