Draped in the clouds of his white spacesuit, James Harris Jackson, 28, trim light hair above a shaved, doughy face, was led in handcuffs out of a police station house in Midtown Manhattan on Thursday morning, then driven downtown for his arraignment.

Prosecutors say Mr. Jackson traveled to New York from Baltimore with a single intention, that of killing black men — no one in particular, just blacks in general — and that he plunged an 18-inch blade into Timothy Caughman, 66, late on Monday evening.

In December 2014, a little more than two years ago, another person crazed over color came to New York, also from Baltimore, and made his way to Brooklyn. That man, Ismaaiyl Brinsley, walked up to the passenger-side window of a police car parked in the Bedford-Stuyvesant section of Brooklyn and emptied a silver semiautomatic handgun, killing officers Wenjian Liu and Rafael Ramos. A few minutes later, Mr. Brinsley turned his gun on himself as he was chased into a subway station. His fixation was neither black, white nor any other hues of human skin; it was blue.

Same motive, different weaponry.

Mr. Jackson, the authorities say, is a white supremacist obsessed with black men mixing with white women; Mr. Brinsley proclaimed himself an avenger of black lives cut down by police officers, and on social media declared his intention to kill some.