In my opinion, there should be no reason a person can't be apprehended, once they've been located and pinned down in a contained location. Even if you can't introduce any measure to incapacitate, I don't see why surroundings can't be fortified for a siege, and the person waited out.
If you're setting up a siege, you're willingly taking the risk that he'll try and break free, killing more people in the process.
Once an area is under control, and authorities are all set up behind sturdy cover, what can the perpetrator reasonably be expected to do that's so dangerous? If someone is cornered in a confined space with limited exit points, drop a couple embrasure'd barriers in front of those exit points and keep them manned with pointed guns ready. What is going to happen? If the person decides to try their luck and make a break for it, they get pathetically sprayed with bullets in an instant, and at that point, I would not have a problem with it. I'm no trained tactical expert, but my imagination cannot conceive of a person being able to pose any appreciable threat, without pulling some unrealistic super spy/Macgyver shit.
I don't what the final situation with this guy looked like, so maybe my logic is not applicable. Maybe this shooter still had full control over a floor of the parking garage. Maybe he had locked himself in a janitor closet. I don't know. When they could arrange for explosives to be delivered to the guy, but not gas or stun, I'm leaning towards the latter.
But there have definitely been situations in the past, like when Christopher Dorner was caught hiding in a mountain cabin all by himself, they had the place surrounded, a three-mile perimeter established, were able to manage the scene for several hours without further injury to anyone while messing about with tear gas and demolition vehicles... but then gave up and decided to burn the place down with him inside.
Oh boy... I think Dallas 7/7 was indeed the start of something big.
Officer shot in the back in St Louis
Officer ambushed responding to a bait 911 call Valdosta, Georgia