Is a person considered complicit in theft if he used a place without its owner's knowledge and saw the owner cut a piece of cloth from it, knowing that the owner swore to inform the shop owner of what he had done, but his truthfulness is doubted?

It is not permissible to sit in a place without the owner's permission, and one must repent from doing so. It is obligatory to condemn whoever steals or takes another's property without their permission, and to inform the owner of the place if the thief persists in their action, especially if lying is their habit. It is not permissible to remain silent about theft, as that constitutes aiding it. It is not permissible to swear by other than Allah, and one must condemn whoever does so. Likewise, it is not permissible to be lenient in fulfilling an oath made by Allah, and worse than that is swearing by Allah falsely.