Mukesh shot dead Sunita Devi yesterday when she came home with Saurabh's body, police said, adding that he is absconding.
According to villagers, Saurabh had accompanied his mother when she was going to offer prayers at the village temple. On the way he stopped to play in a canal, which turned out to be deeper than he thought and started to drown.
Sunita shouted for help, at which some villagers came to their rescue. He was taken to hospital in nearby Bharatpur, but the doctors failed to save his life, police said.
A case of murder has been filed and efforts are on to nab the accused, they said.