Emre Günaydin, Abuzer Yildirim, Hamit Çeker, Salih Gürler and Cuma Özdemir killed two Turkish Christian converts and a German man in Malatya by tying them up and slitting their throats.
President Erdogan called it "savagery" at the time.
The murderers were sentenced nine years later, with three consecutive life sentences each.
The two Turkish victims, Ugur Yüksel and Necati Aydin, were in their 30s. The German man, Tilmann Geske, was 45.
Tilmann Geske and Necati Aydin both had young children and partners, and Ugur Yüksel was engaged.
This week, the Supreme Court upheld the decision of the lower court, saying the men 'deprived the person of liberty' and attempted 'qualified plunder'.
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