The Ukraine International Airlines (UIA) flight crashed shortly after taking off from Tehran.
All 176 people on board were killed.
After initially denying any responsibility for the incident, Iran admitted it had shot down the UIA flight "unintentionally", calling it a "disastrous mistake" by Iran's Revolutionary Guards Corps
Iran's air defences had been on high alert at the time. Hours earlier, the country had fired ballistic missiles at two US bases in Iraq in retaliation for the killing of top Iranian general Qasem Soleimani by a US drone strike in Baghdad.
During a press conference on Sunday, Capt Zanganeh, head of the Civil Aviation Organisation of Iran (CAOI), said "up to 19 seconds" of conversation between two pilots and a pilot instructor had been captured in the aircraft's cabin after the first missile struck.
It was "25 seconds later that the second missile hit the plane", he said, adding: "They were piloting the plane until the last moment."
He said information recorded by the plane's black boxes - which hold key data and communications from the cockpit - indicated that the aircraft had been "in a normal flight corridor" before the first missile exploded, sending shrapnel into the aircraft.
Capt Zanganeh added: "At this moment, the plane has an electrical problem and the auxiliary power of the plane is turned on at the order of the pilot instructor. Both engines were on in the seconds after the explosion.
"No sound was heard from the passenger cabin at that moment... The recording stopped after 19 seconds."
No details of the cockpit conversation were disclosed
Iran had delayed releasing the plane's "black box" voice recorder but in July sent it to France for examination.
No other parties involved in the black box analysis have yet commented.
On 8 January, at 06:12 local time (02:42 GMT), UIA flight PS752 took off from Imam Khomeini International Airport in Tehran.
The plane was a Boeing 737-800 - one of the international airline industry's most widely used aircraft models.
Before leaving the airport's air space, the plane appeared to turn around to return to the runway. Shortly afterwards, it crashed.