Baghdad, Iraq (CNN) -- Gunmen wearing military uniforms stormed houses and killed 25 people in a Sunni village near Baghdad, officials said Saturday.

Five of the dead were women. Most of the victims were shot in the head, and all were found handcuffed, police officials in Baghdad said.

The attack involving at least 20 gunmen took place late Friday in a village in Arab Jabour, a predominantly Sunni region about 15 miles southeast of the capital, authorities said.

The area was once a hotbed of insurgents until the birth of Awakening Councils or the Sons of Iraq, which set about to reduce violence and provide security for residents.

Most of the victims in Friday's attacks were local Sons of Iraq members.

Authorities said the mass shooting appears to be the work of al Qaeda in Iraq but stressed the investigation is ongoing.

Iraqi security forces initially arrested 25 suspects but released several due to insufficient evidence, police said.

Purchasing a military uniform is quite easy in Iraq. In Baghdad, several shops sell police and army uniforms for less than $15.