Now the children of Judah had fought against Jerusalem, and had taken it, and smitten it with the edge of the sword, and set the city on fire. Judges 1.8This verse doesn't say that God had anything to do with the massacre, but the context makes it clear that he did. God chose the tribe of Judah to kill the Canaanites and "delivered them into their hand."
Now after the death of Joshua it came to pass, that the children of Israel asked the LORD, saying, Who shall go up for us against the Canaanites first, to fight against them? And the LORD said, Judah shall go up: behold, I have delivered the land into his hand ... And Judah went up; and the LORD delivered the Canaanites and the Perizzites into their hand. 1:1-4So God deserves the credit (or the blame) for the Jerusalem massacre, along with the other killings in Judges 1.
Since this was just an ordinary massacre, I gave 1000 for the number of victims.
God's next killing: Five massacres, a wedding, and some God-proof iron chariots
Table of God's killings