An investigation into the sudden plunge of the Serbian president's plane last week shows that it was due to the co-pilot spilling coffee on the instruments panel.

The investigation results released Tuesday show that the co-pilot accidentally activated the emergency slot extension when trying to clean the coffee from the panel. That reportedly caused the plane to dive and the brief shutdown of one of the engines. Unsurprisingly there was panic among passengers.

The captain then stabilized the aircraft and returned to the capital Belgrade.

Initially, President Tomislav Nikolic's press office said last Friday that the plane made an emergency return because of an engine failure. Nikolic was en route to the Vatican for an official visit, which was canceled.

Serbia's aviation authorities say that the co-pilot has been suspended.