[Mr. V]

The police were familiar with the boy and his problems.

Misha's family called the police; I have to assume they were in the home snd potentially at risk from Misha when the police arrived?

If so, then I as "the reasonable man" could understand the use of deadly force to protect them from being stabbed.

But if they'd fled, or met the police outside the home upon arrival, then the police would have had the presumably "better" option of quickly retreating when the knife-wielding teen approached them and then await the appearance of mental health professionals to deal with the disturbed young man.