I have dealt with this issue a couple of times. After declaring and notifying the resident that the unit is now abandoned unless they notify me otherwise within a specified period of time (usually 48-72 hours)all items left are now in my property's possession. Since the rent-to-own manager has contacted you and told you there are items, seemingly still valuable, I would exercise caution in claiming them as yours. However, I would not just give it back either. Here's why. Items of a rent-to-own nature may have the rental company's sticker on it, but indeed, the amount of money paid may now be satisfied and the items could belong rightfully and wholely to the resident. So, the rental company manager needs to produce a contract and take the person to small claims court and receive the judgement. He can then give me the court order proving he owns the items and I would give them back. Keep in mind this takes time, so you have to store those items and take good care of them. Otherwise, you might have to pay for them.
The rental company could say they aren't going to all this trouble, so keep it. They will just write it off and sue the resident anyway for a money judgement. Or, you can decide it's not worth the trouble yourself, call the rental company up and tell them to come get the stuff. However, make sure you have legal possession of the unit first. I have known of cases where even though you think and have declared a unit to be abandoned, it turned out the resident was in rehab for 12 weeks and upon returning home, and perhaps finding someone else in their apartment, having never been evicted properly, they sue for all the possessions the property took control of and sold. Oops.