Turkish prosecutors are questioning former chiefs of the army and air and naval forces over an alleged secularist plot to topple Prime Minister Recep Tayyip Erdogan's Islamic-oriented government. The questioning of the retired commanders, including Army Chief Gen. Aytac Yalman, Air Force Chief Gen. Ibrahim Firtina and Navy Chief Adm. Ozden Ornek, on Saturday is expected to shed light on allegations of abandoned coup plots. Several other military officers are already on trial for their alleged role. Some charges are based on excerpts from a diary in 2007 that is said to belong Ornek.