Why did St Paul kill Christians?

Paul was born, raised, and educated as a Jew and became a tent maker like his father. When he came of age, he started studying at the temple under the wise Rabban Gamaliel. Later on, he would come to see the new movement of Christianity (at that time called "the way") as desecrating Judaism and, therefore, viewed it as a threat. Paul then led a crusade to end this "movement" before it really got off the ground. It's important to know that Paul was, for the most part, successful up until his conversion on the road to Damascus.