The bible is a wonderful resource to use. If you are not familiar with it you should take a look at it. I am not sure but there are probably versions of it online and set up so as to be searched for quotes. This process may be both educational for you and useful in your debate. However, you do have the trump card, I do believe. The commandment which says, "Thou shalt not kill." Is pretty clear and simple.
You can quote that back to the person quoting Exodus. You may however need some other quotes and you'd have to do research on that. On the other hand. Why is the bible's quotes so important in the debate? What does it have to offer to the debate anyway? It is not a legal document, and has no legal standing in the courts or in law. In fact the constitutional principal dividing church and state prevents it from having anything more than moral influence.
Are you at a Christian school? Are you debating a team heavily Christian? There are other ways to deal with such. For instance, in the Christian view, God is all forgiving, all loving. How can such a belief support killing people? Especially if a substantial number of them, already executed, have been proven innocent, after they have been killed.
Certainly they can quote Exodus 21:12, but you can counter with, "That is all well and good, but what happens when innocent persons are executed? What then, should not those persons responsible for the death of innocent men and women, themselves be put to death according to your view? Are you saying that if a law enforcement officer, a trial jury, judge and lawyer, a prison system and an executioner all take the life of one innocent person that they all should be put to death?"
Ask them that question and watch their mouths flap uselessly open and shut as their poor addled brain attempts to reconcile that quandary. Then, push that issue.
First however, set them up. Make sure they believe in that Exodus quote. Goad them into making it an important point. Something they cannot retract or retreat from. Talk to them and say, "Let me get this straight, you are saying that because Exodus 21:12 declares that 'any who strike a man down and kills him shall surely be put to death' is an important reason for your supporting the death penalty?" They will of course say yes. You then say, "I just want to be sure, so you are saying that killers should themselves be killed because the bible supports it?" Again, they will agree. So you finally ask, saying this, "Just to be sure I understand you let me pose a story and ask a question: what if my husband were murdered, and I was sure of the killers identity, and I went and killed that person, only to find out later that I was horribly wrong, would I then be subject to the death penalty?" Of course they would say that you were. And so you ask them, "What if two persons helped me with the killing and the hiding of the body and other evidence, would they be subject to capital punishment?" Again they should say yes, or hem and haw about it. You should press them on this point saying: "They helped me kill my husband, it becomes proven that without them I could not have done it, and in fact, in the process they made money out of it, knowingly made a profit off of the wrongful death of an innocent? What then?"
This should have them saying that the partners, indeed would be subject to the penalty. Then you hit them up with the item I mentioned in the second paragraph. I would recommend the set up approach if you can pull it off. The trick is to get their pride and righteous indignation fired up so that they make prideful and absolutist types of statements.
Then you quietly hang them out to dry. Now if they say that you are being ridiculous that there are to many people involved in the legal system and killing them would not be possible, you can counter by asking them about the Nazi's and how it did not seem difficult to take care of a large group of killers through the years
It could be fun. Logic is wonderful is it not?