In the case of pharmacists, cake makers, wedding photographers, etc., I am firmly of the belief that they should not be forced to do anything that violates their religious beliefs.
In this particular case, however, I am just as firmly opposed to this woman’s position.
For anybody to call themselves a Christian, and yet to oppose the death penalty, is a contradiction in terms; and, so far as that point is concerned, their religion is NOT Christianity, regardless of how orthodox it may be in other points. Such people openly and blatantly contradict the God that they claim to serve; for God explicitly commanded the death penalty for murder.
“And surely your blood of your lives will I require; at the hand of every beast will I require it, and at the hand of man; at the hand of every man’s brother will I require the life of man. Whoso sheddeth man’s blood, by man shall his blood be shed: for in the image of God made he man” (Genesis 9:5, 6).
This investigator should be forced to testify, no matter how coercive the means might be.