This question is partially based on a question on workplace but to make it more easily answerable I will specify some of the circumstances more.
Suppose an employee is issued a computer to use for his work. Suppose further that the employment contract allows for reasonable personal use of the computer (if this is not common we can assume that personal use is not strictly forbidden by the contract/internal rules). Suppose that the employee is notified by his superior before termination that he should return the computer in an email that is addressed to the HR and the employee is cc'd on it, where the manager asks HR how the return should be processed. The HR does not respond regarding how to process the return of the computer.
Employee is now no longer employed but has the computer in their possession. They take no steps to return the computer to the company. But they do not actively avoid doing so if the company takes steps to get it back. Is that a crime of any sort?
Suppose that furthermore the employee continues using the computer for personal stuff and allows their family to do so too. Is this a crime of any sort?
Please assume that the original contract is sufficiently vague with regards to how the employee is supposed to actually return equipment given to them, and also probably ignore the various breach of contracts issues in case the company has internal rules regarding any kind of security or safety issues.
For jurisdiction assume US, if state specific, let's go with California.