MAPUTO, Mozambique (AP) — Preliminary investigations into a November plane crash that killed 33 people aboard show that the pilot intentionally brought the Mozambican plane down, an aviation official said.

The Mozambican Airlines plane was bound for Angola with six crewmembers and 27 passengers, including 10 Mozambican, nine Angolans, five Portuguese, and one citizen each from France, Brazil and China, according to the airline. The aircraft went down Nov. 29 in a Namibian national park near the border with Angola.

"There was an intention to crash the plane," Joao Abreu, chairman of the Mozambican Civil Aviation Institute said Saturday after gathering recordings and preliminary investigations.

The pilot's motives are unknown, and investigations will continue, he said, naming the pilot as Herminio dos Santos Fernandes. The co-pilot was in the bathroom at the time, he said.

Radar data showed that, at an obligatory reporting position over northern Botswana, the plane suddenly started to slow downwards rapidly. The plane's movements were normal before that, with no mechanical functions, he said. The altitude selector was then manually altered three times, bringing the plane's altitude down from 38,000 feet to 592 feet, Abreu said, reading the preliminary report to reporters.

Low and high intensity alarm signals can be heard on recovered recordings from the plane, along with the sounds of repeated banging on the cockpit door, he said. The investigation report does not say who was banging, but Abreu asserted that the co-pilot was not in the cockpit at the time of the crash and not responsible for the crash. The "black box" flight recorders were recovered intact and sent to the United States National Transport Safety Board in Washington to be decoded and transcribed.

Other indicators show manual operations were used, he said, adding that "all these operations required detailed knowledge of the plane's controls, and showed a clear intention to crash the aircraft."

The control tower had lost voice and radar contact and set search operations in motion. The wreckage of the plane was found in the following days.