The drone which crashed in Zagreb on 10 March carried an aviation bomb and the cause of the crash was a disrupted automatic landing sequence due to an incomplete connection between the aircraft and the main parachute, the Zagreb County Prosecutor's Office said on Wednesday.

A commission which investigated the crash said the drone ejected the parachute and continued to free fall. During the fall, a mechanism was activated due to which one probe flew out and the other one did not.

Speaking at a press conference, chief air force investigator Mario Pocinok said the drone had been in good condition and the engine was not in operation when it crashed. The black box was considerably damaged, so it was not possible to recover data.

Asked if this meant that the drone did not crash but landed, Brigadier Pocinok said the activation of the auto-landing system depended on the quantity of fuel, the set parametres and the kilometres crossed.

The drone, he added, “was disabled in a way to land. I can’t say there was an error because several elements are missing.”

Asked if Zagreb had been the final target of the drone, Pocinok said it was not up to him to answer that and denied that the NATO secretary general, who claimed earlier that the drone was unarmed, had been informed of the results of the inquiries into the crash.

Major Mile Tomic of the Armed Forces Support Command said 47 pieces of shrapnel, caused by an explosion, and a universal fuse for an aviation bomb with Cyrillic insignia were found at the crash site.

“As soon as the aviation bomb was put into the aerial vehicle, it was not intended for its basic purpose, which was reconnaissance,” he added.

Drone subsequently painted yellow and blue

Ivana Bacic, chief forensic examiner at the Ivan Vucetic Forensic Science Centre, said the crash caused a crater 5.5 metres wide and 1.5 metres deep, and that there was a strong smell of ammonia.

No traces of either military or commercial explosive were found. The original aviation bomb is supposed to contain 40-46 kilograms of TNT.

It has been established beyond doubt that the explosion occurred, and that the aviation bomb contained “a high-energy but unconventional substance that completely decomposed in the explosion, which prevented its identification,” Bacic said.

“On the right wing of the aerial vehicle the dominant colour was red, which reflected a red and white five-pointed star. That was the original colour, and traces were found of subsequent painting into yellow and blue,” she added.

According to her, there was no political pressure on the Ivan Vucetic Forensic Science Centre regarding the findings of the expert analysis.

Asked if Zagreb had been the drone’s final target, county prosecutor Jurica Ilic said he could not answer the question.