Judge Gregory Lasak just did right by Demetrius Blackwell: He sentenced him to life in prison.

In May 2015, Blackwell

ruthlessly killed NYPD Detective Brian Moore

— and tried to kill his partner, too.

The two cops noticed suspicious behavior — Blackwell adjusting his waistband as if he was packing heat. They pulled up to question him; Moore asked if he was carrying. The killer replied, “Yeah, I got something!” and opened fire, hitting Moore in the head.

The cop, just 25, died two days later.

“Mr. Blackwell, you’re nothing but a coward,” the judge told him at Tuesday’s sentencing. “You’re a cold, calculating killer.”

He added, “You’re going to die in prison.”

That is indeed his just reward.