As mentioned, he shot the ground directly in front of himself. Once.
And as mentioned elsewhere here, German police would in that case shoot e.g. a leg to disable the threat, not aim to kill. Someone gave the kill order and a lot of shots were fired. Of course your suggestion to use a sleeping dart (or something similar) would be ideal.
On top of all that but less relevant to this thread, they left the body uncovered on the street until late in the afternoon, approx. 8 hours. I took a lot of pictures of the entire thing (starting after the shooting, because I was afraid the police might think I had a gun too with my huge black camera with telephoto lens).
I honestly don’t believe anyone gave a kill order, I rather feel (maybe not fairly) that police had guns trained on him and heard gun fire and instinctively pulled without even taking a second to analyze situation. If I’m right (good video footage could help prove the theory), this should scare everyone (but likely won’t).
“If a police officer hears and sees the perp’s gun go off, they likely won’t stop to think even long enough to see who got shot, but likely instinctively pull to neutralize the threat.”
In most places outside the US, they’d aim for legs / arms as that would “neutralize” but not “kill”. In this scenario they’ve got snipers trained on him after all, no excuses about handgun accuracy. Yet in the US, you’ll virtually never see that, all shots will be into the chest.
Not clear why a sleeping dart couldn't have been used though. Animal control does a pretty good job in such situations.