If as reported the killer was living with schizophrenia there may not be an easy explanation apart from being off meds. The condition which is presumed to involve an imbalance in brain chemicals that help to transmit brain signals can mean an individuals perception of reality is different to how those around them experience things. They receive sound and light signals through their ears and eyes which are confused in transmission between their brain cells but their brain attempts to make sense out of them leading to their minds reaching conclusions that put them in an alternate reality.
