If a domain is bought and then sold the next year, how do I find out who the original owners was..i.e. the first person to buy the domain.
You can use domaintools.com's domain history service. Here you can view various WHOIS records saved at specific time period. If the whoid was protected, then it is not possible to get the contact information of the old owner.
The person who buy the domain name became the owner of the domain name and nothing to do with the earlier owner, the contact information you can get through whois search unless it is privacy protected.