yeaaa
see if you can't find some solid evidence and call the feds. Missing mail might be probable cause for a judge to issue a warrant to search his property for your mail.
have you considered the possibility that someone other than this individual is stealing your mail? is this person the only other person with access to this mailbox?(like is it locked or something?)
this individual could be found guilty of crimes on both the local and the federal level which means hard time.
On the local level:
"In most cases, being convicted of concealing stolen property is punishable by a maximum of 5 years in prison,"
on the federal level:
“Theft of mail is a felony under federal law, punishable by up to 25 years in prison for each count,” said U.S. Postal Inspector C.K. Aarons.
thats for each piece of mail too!
http://www.ocolly.com/read_story.php?a_id=30612