The scene was a lagoon on the shore of Lake Turkana in Kenya. The time about 10,000 years ago. One group of hunter-gatherers attacked and slaughtered another, leaving the dead with crushed skulls, embedded arrow or spear points, and other devastating wounds.

The dead, said the scientists who reported the discovery Wednesday in the journal Nature, seem to have been scattered in no apparent order, and eventually covered and preserved by sediment from the lake. Of 12 relatively complete skeletons, 10 showed unmistakable signs of violent death, the scientists said. Partial remains of at least 15 other people were found at the site and are thought to have died in the same attack.

The bones at the lake, in northern Kenya, tell a tale of ferocity. One man was hit twice in the head by arrows or small spears and in the knee by a club. A woman, pregnant with a 6- to 9-month-old fetus, was killed by a blow to the head, the fetal skeleton preserved in her abdomen. The position of her hands and feet suggest that she may have been tied up before she was killed.