Punishments were Inflicted by the Witnesses
Source: TTT
Deuteronomy 13:9
Instead, you must surely kill him. Your hand must be the first against him to put him to death, and then the hands of all the people.
Deuteronomy 17:7
The hands of the witnesses shall be the first in putting him to death, and after that, the hands of all the people. So you must purge the evil from among you.
John 8:7
When they continued to question Him, He straightened up and said to them, “Let him who is without sin among you be the first to cast a stone at her.”
Acts 7:58, 59
They dragged him out of the city and began to stone him. Meanwhile the witnesses laid their garments at the feet of a young man named Saul. / While they were stoning him, Stephen appealed, “Lord Jesus, receive my spirit.”