When Joshua and all Israel saw that the men in ambush had captured the city and that smoke was rising from it, they turned around and struck down the men of Ai.

Joshua 8:20
When the men of Ai turned and looked back, the smoke of the city was rising into the sky. They could not escape in any direction, and the troops who had fled to the wilderness now became the pursuers.

Joshua 8:22
Meanwhile, those in the ambush came out of the city against them, and the men of Ai were trapped between the Israelite forces on both sides. So Israel struck them down until no survivor or fugitive remained.

Joshua 10:1
Now Adoni-zedek king of Jerusalem heard that Joshua had captured Ai and devoted it to destruction--doing to Ai and its king as he had done to Jericho and its king--and that the people of Gibeon had made peace with Israel and were living near them.

And when Joshua and all Israel saw that the ambush had taken the city, and that the smoke of the city ascended, then they turned again, and slew the men of Ai.