UST OUTSIDE THE MAIN DOWNTOWN part of Athens lies Kolonos, an old Athenian neighborhood near the archaeological park of Akadimia Platonos, where Plato used to teach. Along the maze of narrow streets, flower-filled balconies hang above open-air markets, and locals gather for hours at lazy sidewalk cafes, sipping demitasse cups of espresso and downing shots of Ouzo in quick gulps.

It was a neighborhood Costas Tsalikidis knew well. He lived at No. 18 Euclid Street, a loft apartment just down the hall from his parents. Slim and dark-haired, with a strong chin and a sly smile, he was born in Athens 38 years earlier to a middle-class family in the construction business.