How could you say it wouldn't work when the citizen in your scenario didn't follow the standard proceedures you described? Not to mention having a gun in his hand when the cops rolled up code 3.
I didn't describe precise procedures in the original post, (except the usual advice to call 911) - I asked what the best would be , because situations do go wrong, and I gave an example in which the citizen did call 911 - but things did go wrong (although partly due to his subsequent error of not staying on the line).
However, I also indicated, you can call 911 and stay on the line etc, do that all correctly - and still be faced with a dire situation. Here's a couple:
1) Before you can call 911 or do anything - one or more screaming cop cars race up, or on-foot cops run up: they had just arrived around the block (or down the block) for a minor call, hear gun shots and race up to you.
There you are... their guns are pointing right at you because they can see you just shot someone.
2) You call 911 and stay on the line. Fine. But after the info about the address and the shots-fired is transmitted, -- the crucial part about you, SD, your description etc. is garbled by static, neither you nor 911 even know that, and cops are there flying out of cars. nor can you tell the on-line 911 operator anything and have her tell the cops, -- no time.
Time just ended.
One can imagine other such situations as well. So the question was what procedures can one follow in addition to calling 911 to avoid getting shot in error.