Alma 18:6

for he had slew many of them, because their brethren had scattered their flocks at the place of water; and thus because they had had their flocks scattered, they were slain.

He had killed many of them because their brothers had scattered their flocks at the place of water. When their flocks had been scattered, they were killed.

He'd killed many of them just because raiders had scattered the flocks at the watering place. That's how it worked—if the flocks got scattered, servants died.