He deposed his elder brother Domenico Gattilusio, threw him in prison, and had him strangled. The Ottoman Sultan Mehmed II used this crime as his pretext to invade Lesbos. According to Franz Babinger, Mehmed's true motivation was that Niccolò had sheltered Catalan pirates in return for a considerable share of their loot; these pirates were preying on the nearby Anatolian coast, kidnapping their inhabitants and selling them as slaves.[1]