The rights group said federal police commander Gen. Mehdi Gharawi is connected to the executions May 3 in a village near Mosul in northern Iraq.
Middle East director for Human Rights Watch Sarah Leah Whitson said Gharawi was dismissed for human rights abuses, including torture, but later reinstated.
"That these killings may have been committed by a unit under a commander once implicated in torture shows why abuses can't be swept under the rug and forgotten," she said in a statement Tuesday.
Human Rights Watch said those allegedly executed were detained by police who swept through the area in early May. The organization said it wasn't clear why authorities arrested any of the villagers, but said some of those detained are being held incommunicado.
Human Rights Watch reported last month at least 40 people died during a security raid on a protest camp in Haweeja, near Kirkuk. The report said Iraqi authorities ordered the raid, though it's unclear if the orders included permission to use deadly force.
"The latest federal police raids and alleged killings show the danger of letting abusive forces run rampant," Whitson said. "The police need to be providing security for the population, not insecurity."