I think this process was completely appropriate. These guys could have proclaimed their innocence even to this crowd, if they could convince them. But they had nothing to say, guilty.

The Talmud (yes that thing that people say is so awful) prescribes 4 kinds of death penalies:
(1) sword (kindest)
(2) asphyxiation
(3) fire
(4) stoning (worst)

Of course these were to be done in public, immediately after the Sanhedrin declared a death sentence.

This shooting is the modern and even less painful version of beheading, the kindest of the execution methods. The Talmud probably called for a worse method of execution for this crime.