Dusseldorf, Sha'ban 26, 1435, Jun 24, 2014, SPA -- Both people on board a Lear jet that crashed after colliding with a German military fighter are believed to be dead, a police spokesman said Tuesday as a criminal investigation was opened against two air force pilots. The 50- and 43-year-old men on board the Lear jet were former military pilots taking part Monday in an exercise with two German Eurofighter jets when the accident took place over the western region of Sauerland. Body parts were found at the crash site outside Olsberg, dpa quoted the spokesman as saying. The men worked for a subsidiary of Airbus Defense and Space and were involved in an exercise on the military response to an unidentified aircraft entering German airspace, said the head of the subsidiary, Klaus Menzel. The company makes 15 flights a day for the military, he said. The Eurofighter involved in the collision was able to land safely at a military base near Cologne despite being severely damaged. It lost a number of parts, including a petrol tank, an air force spokesman said. Prosecutors began investigating the two air force pilots taking part in the exercise for involuntary manslaughter. If a technical problem is found to be responsible for the accident, ground crews could also become a target of the inquiry, a prosecution spokesman said. Investigators were at the crash site, and searches were being conducted for the Lear's flight-data and voice recorders. --SPA 18:46 LOCAL TIME 15:46 GMT www.spa.gov.sa/w