Legal research on sex offenders list

Location: California/New York

I’ve recently become aquatinted with a person who is interested in my business. Upon googling their name social media posts implying the person was a registered sex offender came up. From these it appears that they possibly could have been registered as a sex offender in New York or California. I have found some legal documents about a case where this person was arguing that they did not need to register as a sex offender in New York, which reference another case in which they are said to have to plead guilty to sex offense charges in California, but not the case itself.

Separately I was informed that this person claims they were coerced to plead guilty a there was some form of injustice done to them. How can I do further research on this? I am not familiar with these legal systems or from where I may be able to access decided cases. The alleged sex offense happened in the late 90s while the legal thing in New York in the early 2010s . I just want to know if they did it tbh.