[Blaster86]

18-19 years old is still a stage of cognitive development. They do know right from wrong. They do know when they've made a mistake. People at that age are still prone to making incredibly impulsive and rash decisions without fully grasping how what they are doing will affect themselves and those around them in both the immediate and long term aftermath.

This does not excuse what they have done. They still know right from wrong, but hormones and a lack of developed critical cognitive thinking led them to making a colossal, tragic, possibly unforgivable mistake.