ISTANBUL  For Ahmet Yildiz, a stocky and affable 26-year-old, the choice to live openly as a gay man proved deadly. Prosecutors say his own father hunted him down, traveling more than 600 miles from his hometown to shoot his son in an old neighborhood of Istanbul.

Mr. Yildiz was killed 16 months ago, the victim of what sociologists say is the first gay honor killing in Turkey to surface publicly. He was shot five times as he left his apartment to buy ice cream. A witness said dozens of neighbors watched the killing from their windows, but refused to come forward. His body remained unclaimed by his family, a grievous fate under Muslim custom.

His father, Yahya Yildiz, whose trial in absentia began in September, is on the run and believed to be hiding in northern Iraq.

The case, which has caused a bout of national soul-searching, has underlined the tensions between the secular modern Turkey of cross-dressing pop stars and a more traditionalist Turkey, in which conservative Islam increasingly holds sway.