If it isn't in the Bible, or the Torah, or whatever, how is it a valid source?
And the human sacrifice you're thinking of, is it the guy who said he'd give the first thing he saw at his home to God? Because that was more becoming a nun.
Short answer to the first would be "it's in the Talmud".
Long answer is... I *finally* tracked down where exactly this information was coming from, and it doesn't really fit my case. It is in the Talmud... But not the early pre-Christ versions. Best I can tell, it was added during the revisions that were published between 350-500CE. So there's no real basis for human blood being kosher before that time.
And to be fair, they were probably addressing food that you accidentally bleed into (like from mouth cuts).
Possibly related to this ruling, medieval Jews were often accused of capturing Catholics for blood sacrifices. I've never heard that idea supported by serious historians though, so I seriously doubt it.
I'm done defeating my own point now, back on the offensive.
Despite humans not being kosher according to scripture, scripture does describe them being sacrificed to God. The case you mentioned with the guy returning home to his daughter, is Judges 11:30-40. She didn't become a nun-equivalent (which would have meant being a priest's wife or concubine):
The spirit of the Lord came to Jephthah
He specifically promised God a burnt offering
When he got home and saw his daughter, he lamented (also blamed her)
She begged for two months in the mountains first
When she returned, he "did with her according to his vow which he had vowed"
Just to drive it home, daughters in Israel had a custom of lamenting for her fate 4 days out of every year.
So yeah, he sacrificed her to God by burning. God didn't reject it, or release him from the vow (a thing which exists in Jewish law!). It's implied that the spirit of the Lord inspired him to make the vow in the first place, by appearing to him.
2 Samuel 21, God sends a plague because of Saul. David took 7 of Saul's male descendants and "hanged them in the hill before the LORD", and God ended the plague.
1 Kings 13:2, Josiah is prophesied (by God) to sacrifice enemy priests to God.
And he cried against the altar in the word of the LORD, and said, O altar, altar, thus saith the LORD; Behold, a child shall be born unto the house of David, Josiah by name; and upon thee shall he offer the priests of the high places that burn incense upon thee, and men's bones shall be burnt upon thee.
2 Chronicles 34, Josiah does exactly that, God is pleased.
There are more examples. It's not kosher, but they did it anyway. Maybe humans are exempt from kosher laws because they aren't considered animals or something.