Well by "no questions asked" I'm assuming the context of: 70 people shot by a man in full body armor... man in full body armor caught behind the theater with recently fired weapons... 1 + 1 = 2. What more context do you need?
As for putting a bullet in him, it's called a deterrent. And a lot of the people who already commented about the psychopath wanting to garner attention from this are actually echoing the opinions of FBI profilers and experts that I have heard comment on this and other spree-killings (the difference here, obviously, is that the perp is still living). I believe he is absolutely enjoying the attention and the feeling of power that he gets from this and the longer he lives, the more he gets to enjoy it, which provides a motivation for anyone else with the same goals in mind.
Remove that motivation, add a deterrent, reduce chances of the incident being repeated.
I happen to live in a large metropolitan area where people are killed in smaller acts of violence every day. Literally. Every day. None of the murderers are put to death (I don't even know when the last time the death penalty was applied here). Some of the muderers are caught and placed in prison where they are treated fairly well (many are not first time offenders and have no problem returning to prison). Still more are never caught, or never convicted, and a big reason why is that witnesses are afraid to come forward for fear of retaliation by the criminals. That is called a deterrent. A deterrent in favor of the criminals. Meanwhile, they have no fear of consequences themselves.
I'm a big believer that if you give the criminals more of a reason not to commit crimes, you'll see less crimes being committed. Right now these murderers are counting on the system having mercy on them and making excuses for their behavior, and therefore, they have no fear.