The long, white police truck in Crown Heights, Brooklyn, bears the label “Mobile Command Center” in dark blue letters on the sides. But a more accurate indicator of the truck’s role in the neighborhood can be found by looking down, beneath the truck, at the small drifts of litter and dirt that have swept up around tires long stationary.

The purposes of this and other mobile command centers do not include being mobile very often. They are not intended to race to the scene of a crime, but rather to roll up later and park, a quiet show of force that stays for days, weeks or months, becoming as familiar a part of the block as the buildings around them.

The truck’s quiet place in the background of the city was literally shattered this week, with images of a command center in the Bronx and the bullet hole in the passenger window, the scene of the fatal shooting of Officer Miosotis Familia. She was shot in the head while sitting inside the truck early Wednesday.

The truck, like many of its kind, had been deployed to the neighborhood, Fordham Heights, after a crime — in this case, a series of recent shootings. It had become part of the streetscape, a comfort to some neighbors, an irritant to others. The ambush and murder of Officer Familia sent waves of disbelief and grief throughout the New York Police Department, but it was particularly unsettling to her brother and sister officers regularly assigned to mobile command centers throughout the city. For them, the news hit closer.