Is it necessary to give zakat on income obtained through unlawful means?

If the owner of the income obtained through unlawful means is known, it must be returned to its rightful owner; if the owner is unknown, it should be disposed of by giving it to the poor or to charitable organizations without expecting any reward. (Ibn Abidin, Radd al-Muhtar, 2/291) Therefore, since all of the income obtained unlawfully must be returned to its owner or spent in charity, giving zakat on it is not applicable.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu