If you wish Scripture over Catechism, here's a thought:

Jesus Christ was a victim of Capital Punishment and never condemned it.  The Good Thief said, "We deserve this, but this man (Jesus) was innocent..." Luke 23: 41-43  

St. Paul says in Romans 13: 3-4  
3For rulers are not a cause of fear for good behavior, but for evil. Do you want to have no fear of authority? Do what is good and you will have praise from the same; 4for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath on the one who practices evil. 

It is better not to use Capital Punishment, but it is not intrinsically wrong.  The Church has never totally condemned it in the last 2000 years.
Abortion is always evil.  Not on the same level. 
God bless...