How does Christianity view someone who has killed in the line of duty or self defence (i.e. cop, soldier, etc)?

It can be a great holiness, such risk of life doing one's duty and protecting others.

St John the Baptist did not tell the many soldiers to quit And Jesus complimented the Centurion.

This view (I'm not saying it is your view) is common to ignorant atheists who think that all government is ipso facto evil and son any force or presence of it is to be deplored BUT we are to render unto Caesar , and more than that :

13 Let everyone be subject to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. 2 Consequently, whoever rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves. 3 For rulers hold no terror for those who do right, but for those who do wrong. Do you want to be free from fear of the one in authority? Then do what is right and you will be commended. 4 For the one in authority is God’s servant for your good. But if you do wrong, be afraid, for rulers do not bear the sword for no reason. They are God’s servants, agents of wrath to bring punishment on the wrongdoer. 5 Therefore, it is necessary to submit to the authorities, not only because of possible punishment but also as a matter of conscience.

6 This is also why you pay taxes, for the authorities are God’s servants, who give their full time to governing. 7 Give to everyone what you owe them: If you owe taxes, pay taxes; if revenue, then revenue; if respect, then respect; if honor, then honor.

Thou shalt not kill is clearly hypocritical coming from the guy who wiped out all of humanity in the Flood, or who destroyed Sodom and Gomorrah, or for that matter who had just finished killing all the first borne of Egypt.

I guess he really meant "Thus shalt not kill until I say so"

The commandment thou shall not kill refers to murder or a crime of passion not a crime of defense of the country or law enforcement.( OR RAPES)

numbers 35:16

'If a man strikes someone with an iron object so that he dies, he is a murderer; the murderer shall be put to death.

BIBLE VERSES:

Exodus 21:12

“Whoever strikes a man so that he dies shall be put to death.

Genesis 9:6

“Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image.

Exodus 20:13

“You shall not murder.

Leviticus 24:17

“Whoever takes a human life shall surely be put to death.

No. Self-protection is attempting to maintain your man or woman life or the lives ot others from an attacker who's attempting to harm you or others. homicide is killing somebody else for causes of anger, emotional lack of self assurance, or greed.

Their is nothing wrong with killing another person in self defense if that is what a person needs to do to stop the evil doer.-Jesus Christ

They did what the job demanded or what the circumstances called for. It isn't the same as murder, which is what the Bible forbids.

"Then Jesus said to him: “Return your sword to its place, for all those who take the sword will perish by the sword" (Matthew 26:52. Bible).

killing is killing no matter what its a sin but as long as u ask forgiveness from god im pretty sure he will forgive u as long as ur honest bout it