Well, firstly there's Genesis 9:6
"Whoever sheds human blood,
by humans shall their blood be shed;
for in the image of God
has God made mankind."
Secondly there are different versions of the Bible.
And the Lord spoke all these words: I am the Lord thy God, who brought thee out of the land of Egypt, out of the house of bondage. Thou shalt not have strange gods before me. Thou shalt not make to
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Douay-Rheims Challoner revision 1752
"13 Thou shalt not kill."
And God#GodHebrew: Elohim spoke all these words, saying, I am Jehovah thy God#GodHebrew: Elohim who have brought thee out of the land of Egypt, out of the house of bondage. Thou shalt have no other go
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Darby's Translation 1890
"13 Thou shalt not kill."
Seems like it's more modern books that have decided that "thou shalt not kill" is a little inconvenient. They like killing. Killing animals. Killing criminals etc.
But then that's the problem with the Bible isn't it. Parts of it say one thing, other parts say something else and people pick and choose whatever's convenient for them.