Since the owner of his renting condo let all of his property been used by new tenants. as she said to me she throw all of the

My husband to be is renting a condo and because he got urgent matter he need to come back to his place. And ask his friend that also living there to relay his message to the owner that his going back and also he have 2months deposit and 2 months advance and paid 3rd months after 3 weeks he need to go, for almost 3months But when he come back to his renting condo he was surprise that someone living there and using all of this things that he bought by himself without informing him and when he ask that new living there, He said he's the new tenant on that room and the owner permit him to use all of the things there and also his friend told him that the new tenant is moved there for 1 and half months since he travel. He's been depressed for his situation been from stressful serious family matter going back to his renting space condo to continue his study but when he open the door by his key someone is living there using all of his appliances & furniture's. And for a year now he got many problem mostly about getting into the university. When i call her to try to get important documents She said All Authenticated documents,papers ,clothes and others was already gone because she already gave it to other people. We want to do action for this matter but we don't know what and how.?

how long was she actually gone? can she prove that the owner was informed that she would return?