While this is really interesting to know the fact about Paul. I studied the "New Perspectives of Paul" and understood something which helped me to be clear enough for the above question. Paul is a well-known figure since the first century. Before the conversion, his name was Saul in Hebrew, and Paul in Greek which was given after the conversion. He was Jews (Acts 22:3) as well as Pharisee. Being Pharisee he might be a member of Sanhedrin (the council of 70 members of the high priest). He was there when Stephen was killed Acts 7:58. Saul strongly believed in Torah Mosaic Law. He knows the Scripture and first-century Jews expected the Messiah to be glorious King would come and free them from the hated yoke of Roman domination. But the Hellenistic Diaspore Jews were converting to Christianity and many others. "The Word of God was reaching more and more people. The group of followers in Jerusalem became larger and larger even a big group of Jewish priests believed and obeyed" (Acts 6:7). This was intolerable by the Council as well as Saul. His understanding was people who died on the cross was a curse because he was familiar with the Scripture written in Deuteronomy 21:22, "And if a man has committed a crime punishable by death and he is put to death, and you hang him on a tree, his body shall not remain all night on the tree, but you shall bury him the same day, for a hanged man is cursed by God. You shall not defile your land that the Lord your God is giving you for an inheritance." This verse was the wrong understanding of Saul. He used to think why these people are following Christ who was hung on the cross. This made Saul more offensive because it was blasphemy for them. "And Saul approved of their killing him. On that day a great persecution broke out against then church in Jerusalem, and all except the apostles were scattered throughout Judea and Samaria. Godly men buried Stephen and mourned deeply for him. but Saul began to destroy the church. going from house to house, he dragged off both men and women and put them in prison" (Acts 8:1-3)
Thus, I can say that Paul had a wrong understanding of the Scripture which made him persecute the Christians in the first century before his conversion.