Understand the laws regarding landlord responsibilities.
Landlords usually have two weeks to a month to return the security deposit, depending on state law. If the landlord does not return the security deposit, he is required to send in writing the reasons why all or a portion of the deposit is being withheld, plus an itemized list of the damages and cost of repairs.
Some states require the landlord to put the security deposit in escrow or an interest-bearing account. Upon return of the security deposit he must include the interest.
I may be citing incorrectly but here is a starting point for research purposes, when I sued in California in 1999, my attorney advised me to request the intrest, I won and the interst was awarded as well.
(Sec. 1950.5 (a), (b), (e) and (i) of CC)
oops sorry forgot to add