Katilon Ke Kaatil (1981)

A wealthy woman faces trauma when her husband is killed, and both her young sons abducted. She spends years looking for them, until one day she comes across a young man named Munna, who is wearing a family heirloom around his neck. She accepts him as her son, and takes him to live with her in her palatial house. Then she comes across another young man, Ajit, and accepts him as her elder son. Satisfied that she has both her sons back, she shows Ajit her priceless treasures, which are kept in a vault, and the combination to open the vault. What this lady does not know that neither of these young men are her sons, and their presence in her house is merely to loot the treasure from the vault.