The moon full of Jedi ruins and history has been wiped out by a small mining site. The tools used to mine Kyber crystals out from Jedha City had hit and amplified the power of a Kyber crystal. This wave of energy was sent throughout the ancient city. There are survivors, Imperial and citizen of the moon Jedha, however we do not currently know the casualty count.
Imperial forces had fortunate timing when it came to the accident. A Star Destroyer went into high orbit above the moon to receive more reinforcements. Just hours before that however, a known terror group known as the Partisans attacked an Imperial transport hovertank carrying crystals to an Imperial drop off center. They took out the squad surrounding the tank and the mechanics driving the tank itself. The wreckage shows the Kyber crystal containers empty. We have reason to believe that these terrorists were stealing these to harness it’s destructive energy. They now know the killing power that these crystals are capable of. A number of the group, including its leader Saw Gerrera have been nowhere to be found since the incident. Their attacks may have been a small cause to the explosion and malfunction.
Losing the city was an unfortunate loss but the Imperial Galaxy is one step cleaner since then. Imperials will be returning to this sector to clean and help reunite the planet to the way it was before. No beings should have to live in harsh conditions.