As many as 600 people could have been killed when the Mariupol theater sheltering hundreds of civilians was shelled by Russian forces in March, a new investigation by the Associated Press (AP) reported Wednesday.The Donetsk Academic Regional Drama Theater was hit by a Russian air strike on March 16, killing an unknown number of people inside. The latest AP figure is double earlier estimates released by the Ukrainian government. Researchers based their conclusions on interviews with 23 survivors, rescuers, and other Mariupol citizens, photos and videos taken before and after the airstrike, and feedback from experts. They used this information to create a 3D model of the theater, which they could use to establish where people were sheltering, and how densely crowded each space was. Witnesses told AP that around 1,000 people were inside the theater at the time of the airstrike.

But only 200 people, including rescuers, could be accounted for as managing to escape. Around 21,000 people have died in Mariupol since the start of the war, according to its mayor Vadym Boichenko.

Russian Minister of Defense Sergei Shoigu declared Wednesday that the city was completely under the control of Russian troops.