Sergeant Ahmed Abdelaziz of Iraq’s elite counter-terrorism forces showed reporters on his mobile phone a video, posted by Isis, in which his brother, Saad Abdelaziz, is killed by militants.
Saad was killed in June 2014 at Camp Speicher when militants overran his base. He and more than 1,000 of his comrades killed in the massacre were dumped in a mass grave nearby.
In the most comprehensive analysis on the subject conducted so far, the Associated Press found that there are 72 mass graves left behind by Islamic State militants in Iraq and Syria. Many more are expected to be found as the group cedes territory.
One grave contains hundreds of bodies of people belonging to a single tribe exterminated when Isis militants took control of the region.
Estimates drawn from the memories of survivors, Isis propaganda and an inspection of the graves put the number of known victims buried in mass graves at between 5,200 and 15,000.
Officials say they cannot be sure what the total number of dead is.
Of the 72 mass graves mapped by AP, the smallest contains three bodies. The largest holds several thousand.