A Mozambican airliner that crashed in Namibia last month, killing all 33 people on board, descended with its automatic pilot on and its altitude selector set to below ground level, according to a preliminary report released this weekend.

The report by experts from Namibia’s Transport Ministry said the Mozambique Airlines Embraer ERJ-190, on a November 29 flight from Maputo to Angola, was “flying in normal conditions and no mechanical deficiency was detected” when it suddenly began a descent from its normal cruising altitude.

It crashed in a Namibian game park, killing the 27 passengers and six crew on board.

The report, released to media by Mozambique’s Civil Aviation Institute at the weekend and based on the plane’s black box flight recordings, said the fact that the aircraft made the descent on autopilot, and after actions that would have required knowledge of its systems, denoted a “clear intention”.

But the document, seen by Reuters, did not spell out what this intention was and added “the reason for all these actions is unknown and the investigation is continuing”.

According to the report, the flight recordings showed changes to the plane’s speed and altitude had been made manually, including the altitude selector being set it to a level below ground level.

It said the commander, Herminio dos Santos, was alone in the cockpit at the time of the crash, after his co-pilot had gone to the bathroom. Alarms going off could be heard on the flight recordings, and also the sound of someone beating on the cockpit door “as if asking to be let in”, it added.

Asked by journalists in Maputo whether the report meant dos Santos had deliberately crashed the plane, Mozambique’s civil aviation chief Joao Abreu declined to give an answer.

Asked the same question, Mozambique’s Transport Ministry spokesman Verlopes Nhampossa told Reuters the Mozambican government and civil aviation authorities were not in a position to “make interpretations” of the experts’ report.

The plane’s manufacturer, Brazilian aerospace conglomerate Embraer, said at the time of the crash the aircraft had been delivered to Mozambique Airlines in November 2012.

Besides the crew, the passengers who died in last month’s crash included 10 Mozambicans, nine Angolans, five Portuguese, one French, one Brazilian and one Chinese.

(Reporting by Manuel Mucari; Writing by Tiisetso Motsoeneng and Pascal Fletcher; Editing by Andrew Roche)