He was a Marine buddy of Casey's, the one she told on 7/16/08 that she was planning a trip to California to come see him and needed to tell him something. She told him her mother and brother knew, but she wasn`t sure how he would react. Hmmmm....
Here's some more background by another site if you'd like to read up on him:
Let's recall Mark Hawkins. Our Marine who at one time was in California. (to whom some of us suspected Casey was going to bolt to during the "give me one more day" plea to Cindy on the 911 tapes)
It appears that Mark Hawkins' ex is the "Tara" mentioned in one of the jail visitation videos between Cindy and Casey-when Cindy asked "Do you trust Tara" and Casey says "NO! She's a psycho!"
According to Lee's blogs and other sources, apparently, Tara was pregnant by Lee and went back to Mark and told Mark the baby was his. She then got an abortion, never told Lee, divorced Mark, and is now in Michigan with yet another man, possibly her now husband. I have also read that Casey, before all of this, had an affair with Mark which resulted in Caylee. (my note: he claims in his interview while they did date they were not intimate. JMO but I don't think he's being truthful in that answer

)
http://spoiledmom-mommyconfessions.blogspot.com/2008/12/lee-anthonys-blogs-just-when-you.html
http://humbleopinionforum.net/2011/03/11/mark-hawkins-statement-with-ncis-about-casey-anthony/
http://www.docstoc.com/docs/73478924/Casey-Anthony-Mark-Hawkins-NCIS-document-March-11-2011