Help required. Is Anyone aware how does third party BGC checker - Matrix (hired by TCS) works ?

I have been working in company for 10+ years and now moving to different project now and they are doing fresh BGC, I don’t know why as It was already done when i joined TCS. I submitted all required documents that time.I want to understand, how these third party vendors who does BGC, checks our criminal records and previous employment details? If anyone is having criminal record, how do they check it? Should we mention it?