Get serious. Most Christians understand that the state has the right, under God and without contravention of Ex 20:13, to administer the death penalty to, inter alia Scott Peterson. Moreover, most Christians understand that we have the right to use deadly force in a just war and in just law enforcement without contravention of Ex 20:13. [I believe that even phantasmagorical RCC dogma would allow that.]
So, the citation of Ex 20:13 (more properly translated "You shall not murder") begins the inquiry, it does not end it. Those who glibly cite Ex 20:13 for support of their political argument are really echoing unsupported RCC dogma, not the Scriptures.
You have the GALL to compare Terri's plight with SCOTT PETERSON?????????
Sad to be you.
"Whoso sheddeth man's blood, by man shall his blood be shed: for in the image of God made he man".
And Romans 13:4b:
"But if thou do that which is evil, be afraid; for he beareth not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that doeth evil."
Both of these verses, and others, lend support to what you've said.