And no believer can kill a believer except by mistake; and whoever kills a believer by mistake, then he should free a believing slave and deliver a good ransom to his family except they remit it freely. And if he is from an enemy people to you and he is a believer, then should free a believing slave, while if he is from a people with whom you have a treaty, then deliver a good ransom to his family and free a believing slave. Then if anyone is unable to free a slave, then he should fast for two months uninterruptedly, as repentance from Lord Allah, and Allah is the All-Knowing, Wise.
Today, as there is no group of believers anywhere in the world, there is no war and killing. The believer who considers the Lord as the Impartial does not kill any soul except with Truth as told in verse 25: 68. Remember that without Adhikr nobody can become a believer as explained in verse 10: 100. The burden of bloodshed, killing, terrorism, and all such mischievous activities happening anywhere in the world should be borne by the Arabic Quran reading Fujjar who hide and reject Adhikr. The Fujjar are denoted as the worst creatures among thousand communities of Lord's creatures who don't utilize their intelligence as explained in verse 8: 22. See explanation 2: 2-5, 30, and 3: 183.