Have him sign a Return of Possession form that documents the date he is returning possession back to you.

I had another thought - if I was you, I would email him and tell him that you do not want photos of the interior of your apartment that show your personal possessions made public in any way, because you are concerned about someone burglarizing your home.That way, he can't just post your personal possessions on realtor.com or Craiglist with the address to where someone can find you lovely, expensive MacBook Pro, for instance.And then if you are burglarized, he gets to pay your renter's insurance deductible, since you forewarned him of your concern. 

In the end, if they don't move out, I will have to pursue the eviction route to get possession of the property.

He took possession Feb 1st, and has had no problem until today. 

This means, that if a tenant breaks a lease, you're required to try to find a new tenant asap using reasonable means, and can only continue charging the tenant rent until you get a new tenant in the unit.But, this does not give you the right to take possession before they have defaulted, in my opinion. 

I might call the previous tenant myself and ask if they would return the package I know they have in their possession. 

All parties are jointly and severally liable (provided the lease states such) until you regain possession of the unit or you negotiate with them to change the lease to release one person and/or add another.  

The best course of action right now is to get possession as quickly as possible so you can get it back on the market.

Some courts might think that the text message is sufficient to effect the transfer of possession back to the landlord, but I personally wouldn't risk it.

In other words, don't be nit picky, allow them the freedom to live there much in same manner as they could if they owned, after all that is what you leased, owner's rights of possession.