He slowly eases his vehicle out into the alley of a precinct in Seattle (population: 684,451), scanning left and right as the precinct’s metal garage door trundles down behind him.

The brick alley has recessed alcoves that could conceal someone lying in wait, and the new safety protocol in his department says to take no chances, make no assumptions and avoid being predictable.

“One of the most vulnerable times in our day is shift change,” Officer Virgilio, 31, says as he checks the route. “It’s a matter of avoiding certain patterns. Anybody who is trying to organize some sort of attack on police officers is going to do some sort of surveillance. They’re going to figure out when our shift changes are, they are going to figure out what doors we use to get in and out of the precinct. And it doesn’t take long to gather that type of intelligence.”

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Lt. Scott Finn begins all his shifts in Prince George’s County, Md. (population: 909,535), a densely packed suburb just outside Washington, D.C., by passing through a set of doors scarred by two bullet holes, each a round shock of silver, embedded in mundane tan paint.

A few months before the ambushes in Dallas and Baton Rouge, a man with a semi-automatic handgun opened fire outside the police station in Landover as officers were leaving roll call. With two of his brothers filming, the police said, the man shot randomly at cars and an ambulance, while officers inside the stationhouse returned fire.

A 28-year-old off-duty police detective, Jacai Colson — who, like the gunman, was black and dressed in street clothes — happened to pull up to the front of the station, on his way into work. A fellow officer mistook him for the assailant and shot him dead.

“It was just the fog of war,” Lieutenant Finn says. “Everything had to align perfectly to have something like that happen.”