Legal research can be time-consuming and expensive. Google is a good, cost-effective place to start.
You should speak in confidence with an attorney as he/she will guide you in the right direction.
I'm not understanding your question. Are you asking for access to your own (or the other parents) ACS history (i.e., your casefiles)? If yes, you can ask the Court to order a court-ordered investigation ("COI"). If you are asking for legal research, then you'd need to hit the Law Library - there's one at Bronx Supreme Court.
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If you have actually filed a custody case, you can ask that the court order a COI (court ordered investigation). That will include basic information about any prior child protective history of both parties. Otherwise, if the case is going to trial, your attorney can subpoena records. If you don't have an attorney, you are making a big mistake.