I sent money via Western Union for a friend and it has been flagged. I don’t what it was for. Now he’s angry it did not go through. He's threatening my son and me. What should I do? I’m supposed to call Western Union. I’m worried. Should I contact the police or the FBI?
If your "friend" is threatening your son and you, you go straight to the police.
If this "friend" is not someone who you have known in person for a long time, then it is quite possible and even likely that the "sending money for your friend" is some kind of scam. So: Call the police, and call Western Union.
If Western Union "flagged" this transaction, that means the transaction followed a pattern that in their experience is some scam.