How could David take Goliath’s head to Jerusalem if the city had not yet been captured?

The caputre of the city happened later, as recorded in 2 Samuel 5:6–10. The mention of David taking Goliath’s head to Jerusalem is most likely a parenthetical statement inserted by the author.¹ With the narrative being composed and edited sometime after the events that they describe, the author would sometimes place events that occur at a later time² into the text as if they had already happened, or at a point where he thinks it would be most appropriate to convey a particular message.