HOW COULD DAVID TAKE GOLIATH'S HEAD TO JERUSALEM?

I Samuel 17:54. And David took the head of the Philistine [Goliath], and brought it to Jerusalem; but he put his armour in his tent. (KJV)

Note: The assumption of contradiction is that David had not yet conquered Jerusalem. While it's true that David had yet to conquer Jerusalem, this hardly means that David could not have had a tent there.  The Israelites could have been in charge of Jerusalem at that point and later lost it, necessitating David's capture of Jerusalem.  Or it could have been held by people who didn't object to an Israelite having a tent there.  Either way, not a contradiction.