Luck?
Come out from under your bridge and elaboratePossibly with a big enough concussive force.
You could also maybe roast them. I think you could possibly heat the suit up enough to cook the guy inside without damaging the electronics.
Or if you could get close enough to twist the guy's neck until it snaps. Unless the helmet has some sort of locking mechanism to prevent that.
With concussive force you could maybe knock them out, killing them may be a stretch. Unless you beadt them into the floor. If you think about it, a gunshot is concussive force when you're wrapped in a giant tin-can which doesnt let the bullet through, it would have to be a pretty damn big concussive force. A tank maybe? PA is "capable of absorbing over 2500 Joules of kinetic impact" remember.
As far as heating them up goes, i could see that working. But "The 10-micron-thick silver ablative coating can reflect laser and other radiation emissions " so a working suit wouldnt be affected.
And neck snapping, well.... Youd have to be pretty damn strong. But possible, maybe.
So all of those options may well be possible, but without nigh on destroying the suit? Not so much