I'm quite certain Nico Robin is involved as she's the only one who had opportunity.

Only pirates have motive, means, or knowledge of the cuffs to care and the Malnosso aren't in the habit of taking items already in possession by us away. Furthermore, the Whitebeard commanders purloined my jitte before, so don't impugn my investigation efforts. I didn't simply jump to the gun, I spent several days investigating before demanding the return.