The story
Probably related to claw (compare Low German kleien, klaien (“to claw, scratch, grasp, seize”), dialectal German klauen, kläuen, kleuen (“to steal”), German klauen (“to steal, rip off”)). Alternatively referred by some to Dutch kleed (“a garment”); "to fake a cly" was to take a garment.
Etymology from Wiktionary, CC BY-SA 4.0.