Why did the police sniper appear and how do I pass him?

I'm playing what I presume is the 'boss level' of the game Gunpoint. I've done everything and it remains to escape to the subway station on the right, however there's a police sniper there.
Why did the police sniper appear (he wasn't there at the start), and how do I pass him?
Best Answer
I think the police sniper appears if you shoot the gun (I did that to break a window). Then there's a 60 second counter in the corner until the police sniper arrives.
A police sniper. Kills instantly at any range. You may be boned.
Looks like you have to restart the level.
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Answer 2
The police sniper appears after you fire your gun. Your best bet is to go back through your checkpoints until you reload a state before you fired your gun.
Answer 3
The police sniper appeared because you fired your gun (resolver). After you fire, a countdown timer appears, at the end of which the police sniper appears at the exit.
I dealt with the police sniper by firing at them from the same height, on the ground to the left of the building. Since all the doors in the ground floor of the building were gone, the bullet went straight through and killed the sniper. Why the protagonist wasn't killed in spite of presumably being in the firing range of the sniper, I don't know.
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