The blaze ripped through a venue hosting a large crowd of people on Tuesday in the town of Hamdaniya, also known as Qaraqosh, in the northern province of Ninevah.
Earlier this week, authorities said that indoor fireworks had set alight ceiling decorations and engulfed the hall, built from highly combustible materials.
The venue was designed for a capacity of 400, but the owner and three staff members had allowed 900 people to attend, the probe found.
“The fire was accidental and unintentional and occurred due to gross negligence,” the findings said.
The results of the investigation were announced by Interior Minister Abdul Amir al-Shammari at a news conference on Sunday.
“Using flammable decoration helped the fire spread quickly and transformed the hall into a fireball,” Shammari stated.
He added that the blaze trapped people inside the hall and that rescue teams struggled to reach them due to there being only a few small doors.
At least 150 people were wounded during the fire, suffering from burns, smoke inhalation and crush injuries when trying to flee the scene.
An eyewitness, 55-year-old Amer Karoomi Hanna, told Middle East Eye on Wednesday that he was at home when he heard about the fire.
“I arrived at 10.30pm and the fire was still raging in the hall. My friends had told me about it and I came quickly. I have no relatives, but everyone is like family in Qaraqosh. There are no strangers in this town,” he stated.
“I saw people walking around, tired, trying to extract the wounded. There was a large number of people in the hall,” he added.
The investigation recommended that legal action be taken against local officials.
Iraqi Prime Minister Mohammed Shia al-Sudani visited victims on Thursday and said he would hold those responsible to account.
At least 14 people, including the venue owner, 10 employees and three people suspected of setting off fireworks, were arrested by authorities.
Hamdaniyah is home to 26,000 Christians and is one of the main centres of Iraq’s Christian community.
