Saul asked the high priest to authorize him to arrest believers.

Acts 9:1-2

9 Meanwhile, Saul angrily continued to say, “I will kill those who believe that Jesus is the Lord!” He went to the supreme priest in Jerusalem 2 and requested him to write letters introducing him to the leaders of [MTY] the Jewish meeting places in Damascus city. The letters asked them to authorize Saul to seize any men or women who followed the way that Jesus had taught, and to take them as prisoners to Jerusalem so that the Jewish leaders could judge and punish them.