A passenger plane carrying 67 people, traveling from Baku, Azerbaijian, to Grozny, Russia, crashed on Wednesday on the shore of the Caspian Sea near Aktau in Kazakhstan. Thirty-eight passengers died but 29 passengers and crew members survived. Most of the plane’s fuselage was severely burned.

Investigators from Azerbaijan, Kazakhstan and Russia have opened criminal inquiries to determine what caused the crash. In Azerbaijan, investigators believe that a Russian Pantsir-S1 air defense system damaged the plane, which was in the vicinity of Grozny, according to two people in Baku, who were briefed on the inquiry and spoke anonymously because it was ongoing.

The Russian authorities said the plane had been diverted from its original path and have offered differing explanations for why. At first, they said that the flight was diverted because of fog and that the plane was hit by birds. On Friday they said the airspace around the Grozny airport had needed to be cleared because of Ukrainian drones. They also said the plane had made two failed attempts to land in Grozny.

Also on Friday, some lawmakers in Azerbaijan demanded that Russia apologize for the incident and conduct a thorough investigation.

Here is what we know about the crash.

The plane was on a regular flight to Grozny.

Operated by Azerbaijan Airlines, the Embraer 190 airliner was making a regular flight on Wednesday from Bazu to Grozny, the capital of Chechnya in Russia, on the other side of the Caucasus Mountains. That morning, aerial battles between drones, launched by Ukraine, and Russian air defense systems were taking place in the area around Grozny and across the North Caucasus, according to residents and local news media reports.