Tell me, have YOU murdered anyone? Yet, wouldn't you admit that you HAVE sinned? The FACT is that we ALL have sinned and FALL SHORT OF THE GLORY OF GOD. That is the message of Romans 3. It isn't saying we are only sinners if we've killed someone. It is God telling us we can NEVER be as perfect and sinless as He is. That can only come from Christ's imputed righteousness given to us by the grace of God through faith. Mary admitted she needed a Savior, so should we.
St. Jerome, doctor of the Holy Church, thee who gave us the Latin Bible, pray for us.
In the name of the Father, and of the Son, and of the Holy Ghost, amen.