Below are several useful OSINT tools that can assist researchers in discovering data connections across different verticals. While I hope people coming across this page use these tools with care and with ethical goals in mind, the truth is that sophisticated criminals are often able to outsmart common research methods, which is why government agencies (and not OSINT) are the appropriate entities to investigate them, rather than hobbyists. Be sure to protect yourself at least somewhat if you are exposing fraud or corruption, etc.
Web page archiving:
Social media mapping: