"We decided immediately after the assassination to establish a commission of inquiry, and (its conclusions are that) the Mossad is behind the assassination," a Hamas official said in a press conference in Beirut.
"There was an internal debate in Hamas on whether or not to release the results of the investigation, and eventually we decided there is no option but to make the conclusions public, because the Mossad is behind many assassinations from Abu Jihad (Fatah co-founder Khalil al-Wazir) to Imad Mughniyah (senior Hezbollah member)," the Hamas statement added.
According to the Hamas inquiry commission, preparations began a year and a half before the assassination when a female European journalist with a Hungarian passport contacted al-Zawahri to obtain information from him. Hamas claimed al-Zawahri refused to cooperate, because he was suspicious of her.
The logistical preparations for the assassination, according to Hamas, began four months prior to the execution of the plan.
The cell that killed al-Zawahri allegedly rented an apartment and two cars, with the assassins entering Tunisia with a Bosnian passport.
On the day of the assassination, the cell followed al-Zawahri as he left a clinic. The assassins reportedly used one car to ram into the Hamas engineer's car, and then exited their vehicle and shot him.
The commander of the operation was a man called Yohan, according to Hamas, and there were three cells, including one in charge of logistics and another in charge of carrying out the actual assassination.
Hamas confirmed al-Zawahri's ties to the group on the day after the assassination. "Al-Zawahri joined the Izz ad-Din al-Qassam Brigades a decade ago. He acted against Israel in defense of Palestine and was one of the commanders who supervised our UAV program," the organization said in a statement.
The drone engineer's wife, Majdah Khaled Salah, told Al-Jazeera about his alleged assassination.
"At approximately 1:50am we heard gunshots. I got out the door and started to run, I thought at first it was a gas explosion. But when I ran outside, I saw my husband's car smashed in from the back. I ran around to the other side of the car, and I found my husband. I called out to my husband, calling him by his other name 'Murad.' I said 'Murad, answer me!' I put my hand on his heart and his clothes were full of blood. His phone fell into my hand. The bullet hit his heart. It was one bullet to the heart and another to the throat," she recounted.