Gideon had threescore and ten sons of his body begotten: for he had many wives. And his concubine that was in Shechem, she also bare him a son, whose name he called Abimelech. Judges 8:30-31Which was a problem since only one son could succeed him. Luckily, Abimelech came up with a creative solution. He killed all of his 70 brothers on one stone.
Abimelech ... went unto his father's house at Ophrah, and slew his brethren the sons of Jerubbaal, being threescore and ten persons, upon one stone. Judges 9:4-5Well, all except one, anyway. Jotham, Gideon's youngest son, got away.
So the two remaining sons, Abimelech and Jotham, schemed against each other for control of Israel, with Abimelech winning out, becoming Israel's first king.
Then God decided to get involved by sending an evil spirit.
God sent an evil spirit between Abimelech and the men of Shechem; and the men of Shechem dealt treacherously with Abimelech: That the cruelty done to the threescore and ten sons of Jerubbaal might come, and their blood be laid upon Abimelech their brother, which slew them; and upon the men of Shechem, which aided him in the killing of his brethren. Judges 9:23-24(Now you might think it strange that an evil spirit would be sent by God. But if so, you haven't been reading your Bible enough. The Bible is clear about evil spirits: they are either sent directly by God or their origin is unknown. The Bible never attributes evil spirits to Satan.)
Things get complicated after God's evil spirit arrives. But the short story is that Shechem revolts against Abimelech and Abimelech massacres everyone in Shechem, except for 1000 that escape to a tower.(See the Brick Testament story for the details.)
When Abimelech found about about the people in the tower, he set it on fire. While the tower was burning, a woman dropped a millstone and it landed on Abimelech's head, crushing his skull. Abimelech saw that it was a woman, so he told a soldier to kill him since he didn't want it said that he was killed by a woman. (In the Bible, there's nothing worse that being killed by a woman.)
So with the help of God's evil spirit, everything worked out according to God's plan.
Thus God rendered the wickedness of Abimelech, which he did unto his father, in slaying his seventy brethren: And all the evil of the men of Shechem did God render upon their heads: and upon them came the curse of Jotham. Judges 9:56-57
Note: I missed this one up to now, so I'm going to have to revise the list. I estimated a total of 2001: 1000 in the burning tower, 1000 in the Shechem massacre, and Abimelech (who wasn't killed by a woman). I know the 2001 value is silly and arbitrary in its precision, but any attempt to put a number on God's killings will run into the same problem.
God's next killing: The Ammonite massacre