PITTSBURGH (KDKA) — The tragedy in Canonsburg is part of a terrifying and disturbing national trend of the ambush shootings of police officers.

Just last week, police in three cities were gunned down in surprise attacks.

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It’s a truth known by all in law enforcement, there are no routine calls. A domestic disturbance like the one Thursday morning can result in a deadly attack on the responding police officers.

“They have to approach the house, they have to knock on the door to try to determine… but if somebody decides they want to ambush the officer, they can just lie in wait and they can pick the moment of attack, and that’s what makes this job very dangerous for police officers,” said Bob Swartzwelder, the head of the Pittsburgh FOP.

Police shootings are on a horrifying rise. Fifty-three officers have been shot and killed this year, compared to 33 this time last year. Many of those officers were ambushed.

Ambush shootings of police are up 300 percent as Officer Scott Bashioum becomes the nation’s 15th police officer to be killed this year in a surprise attack.

Swartzwelder says these ambush killings have ushered in a terrifying era for police.

“Louisiana this year, Dallas this year, all of these different attacks that have occurred this year, massive ambush attacks on law enforcement. That’s why I keep telling everybody we’re looking not like the United States; we’re starting to look like developing countries or countries that are in conflict,” says Swartzwelder.

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Domestic calls like the one in Canonsburg can be especially volatile, but Sheriff Bill Mullen says there are no safe ones.

“You’re not really quite sure about any call. You could be ambushed or you could just be taking a report,” he says.

Police rely on advanced word from emergency dispatchers as to whether there is a prior history of problems at an address or whether a suspect is armed.

But Sheriff Mullen says there is no way to be absolutely sure.

Sheriff Mullen: “The bottom line is you’re still going to have to go up to that door and you don’t know what’s behind it. Even getting out of the car, getting out of the police car.”

KDKA’s Andy Sheehan: “Anything can happen?”

Sheriff Mullen: “Anything can happen.”

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These police ambush shootings are a terrifying and disturbing trend across the country, proving that no call is routine, no area is immune and no police officer is every out of harm’s way.