Images and reports from the crash site, just outside the Iranian capital, Tehran, show at least one bulldozer working in the debris at the site, where the Boeing 737-800 crashed Wednesday morning, killing all 176 people on board.

The crash site is at the center of a tense geopolitical struggle over exactly what brought down the jet, which was operated by Ukrainian International Airlines…

Physical evidence from the crash site could provide more information about what happened, but the usefulness of the evidence could be compromised if it is disturbed.

Giancarlo Fiorella, a researcher for the investigative website Bellingcat, shared a thread of photos that he said showed heavy machinery at work.