You might find helpful my Legal Guide "How to Organize Your Small Claims Case Testimony"
God bless. I note that you might check to see if your damages are within the small claims court jurisdiction.
You don't need to do it yourself.
Basically all violations of the security deposit law fall under MGL 186 s15B. That statute provides for automatic attorneys fees, and (in many cases) also provides for automatic triple damages. Also, because the statute is complex yet specific, in most cases the violation is easy to prove.
Because the attorneys fees are mandated by statute, most attorneys who work in this area will generally take these cases on a contingent fee basis. You won't have to pay up front, because the landlord will be liable for attorneys fees when they lose.
So my advice is that you find a landlord/tenant attorney and "hire" them (you should not have to pay any legal fees up front, though some attorneys will ask you to pay the filing fee.) They will probably want to go to district court, because it permits them to win on a motion for summary judgment--that's what I usually do, in any case.
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