Ex-Roomate Stole and Modified My Check, Law Enforcement and Bank Not Helping

My question involves criminal law for the state of: New York (Nassau County)

This is a somewhat complicated story so I will try to make it as clear as possible. I'm beyond frustrated at this point, and any advice would be MUCH appreciated. I am a single mom and graduate student so my time and financial resources are limited, which is why any advice here would be very valuable to me.

My roommate moved out of my house (house I rent, and act as "sub-landlord", I don't own it), and when she did, I told her that I had 30 days to return her security deposit via certified mail. We agreed to deduct the amount for bills that she owed (when I got them in the mail) out of her security. During the 30 days she emailed me several times asking repeatedly what the bills were and when she was getting her security back. I was always responsive and basically told her I had 30 days to return it. Toward the end of the 30 days, I emailed her the total she owed in bills. I remembered her saying that she had paid a cable bill and was owed for it, so I asked her to give me proof of payment which I would deduct and then cut her a check and mail it out. I didn't hear from her, which was odd.

A few days later, I am looking in my account and notice a check written out for $650 (the amount of her security deposit). After some investigation it became apparent that she had stolen the check out of my check book (a few months earlier). Here is the complicated part, the check was PARTIALLY filled out by me. I had written her name in the "to" line, and it was dated in June 2011, and the memo line said "Cablevision", and it was signed by me. The dollar amount was left blank (she filled this in her handwriting for $650). This jogged my memory and I recalled starting to fill out the check for her (for that cable bill she said she paid) but I didn't receive a total from her, so I left it temporarily in my checkbook. She must have immediately stolen it (back in June) and held onto the check.

I have the original carbon copy which I compared to the digital scan from the bank, and it is obvious that she changed the date from June to August (changed a 6 to an 8) and because the memo said "Cablevision" clearly I didn't authorize it to be filled out for $650. At first the bank froze my account to investigate, but they refused to refund my money because the signature on the check was mine.

On the bank's recommendation I filled out a police report, the police at the counter said I had all of the evidence and that she would be arrested for 3 counts of larceny (I believe), including falsification of a business document. I waited patiently for the detective to contact me, and for her to come and turn herself in at the station. Several weeks went by and finally the detective said he had interviewed her and wanted to interview me. When I got there he said that she had admitted to stealing the check, filling out the amount and changing the date but that her actions were "on the border" of being civil and criminal. He agreed that she went about it in the wrong way, but he did not arrest her.

In my impression he didn't want to waste his time, he specifically told me about another check fraud case he has for $30,000. Ultimately, he said he would try to help me, by going out of his way, and telling her to pay me the amount that she owes me in bills, and that I should just "drop it". Though upset, I emailed her again asking her to pay me the approx. $350 she owes me for my bank fees, pro-rated extra days she lived at my house, and the bills. She wrote back arguing the amount with me and saying she would send me a check for $50. If she had sent me the full $350 she owes me, I probably would have just dropped it, but the fact that she is now arguing with me about the total just adds insult to injury.

I am furious that it seems like she will completely get away with stealing and modifying a check of mine with out my permission. The way I see it, she stole from me. It doesn't matter that she "thinks" I owe her a certain amount, she went about it in the wrong way, and I think she should face consequences for her actions. This girl is in school for pre-law so she has this attitude that she knows what she is doing, and is above the law. At this point, should I call the detective again and complain, ask for his supervisor? Get a lawyer? Call the District Attorney? No idea how (or if even) to proceed. Thank you again for reading and in advance for any advice and help.

CONDENSED VERSION: Ex-roommate stole a partially filled out check from my checkbook. Modified the date and added an amount ($650) that I did not authorize. Law enforcement said it's on the border of civil/criminal and are not helping to persecute her. Should I pursue further? Who to contact next?

You have already contacted the appropriate authorities. They deemed your case not worth pursuing.

If the police officer does not believe it's worth pursuing in criminal court, you can try talking to his supervisor or to somebody at the prosecutor's office.

You can also consider suing in small claims court.

Incidentally, "Landlords, regardless of the number of units in the building, must treat the deposits as trust funds belonging to their tenants and they may not commingle deposits with their own money." If you bounced checks because you commingled your tenant's security deposit with your own money and then spent it, that's not proper handling of the deposit.

Thank you for your response. I did not bounce any checks as a result of her actions. The issue with bank fees occurred because the account that she deposited the check from was linked to my personal account. "Her" money was in a separate account.

So besides taking her to small claims court for the money she owes me, you don't think there is a criminal case against her despite the fact that she stole and admitted modifying the date and amount on my check with out my permission? I found a Criminal Complaint form I can file with the District Attorney. Besides contacting the detective again, I suppose my last resort (other than small claims) is to fill out this form and bring it to the DA.