An American tank burst through the walls of the Doctors Without Borders hospital accidentally bombed in Kunduz, Afghanistan Thursday and–according to medical nonprofit Doctors Without Borders–potentially flattened evidence of war crimes.

The tank was sent by a joint U.S.-NATO-Afghan team investigating the Oct. 3 bombing that killed 22 patients and hospital staff, including children. After the “intrusion” Thursday, Doctors Without Borders said, “[The tank’s] unannounced and forced entry damaged property, destroyed potential evidence and caused stress and fear.”

The charity was not told beforehand that a tank would be rumbling through the ruins of its hospital.

In the aftermath of the bombing, American military officials asserted that the airstrike was carried out at the request of Afghan ground forces. The Pentagon is currently issuing ‘condolence payments’ to the families of the victims.