Scott Peterson Case: Truth be Told: If not Scott, then who did it? Part 1 does an excellent job of showing that by Todd's own words, he had to be on Covena on the 24th between 10:35 and 10:50 a.m.
To further illustrate, this first picture shows a very similar mailbox offered on http://www.home-improvement-superstore.com.
This second picture shows the actual mailbox with manila envelopes the same size as the mail that was put out by Susan Medina on the 24th. Susan's outgoing mail consisted of blank forms, thus no need for privacy. The incoming mail, however, would be the completed forms and other sensitive mail for her work. Thus the need for the incoming mail to be under lock and key. When you open the flap, there is a slot that the mailman drops the incoming mail through, to fall into the bottom locked box. Graybill said he had to first remove the outgoing mail, and then deposit the incoming mail. As stated on the Facebook page, Todd would have seen the outgoing mail sticking out, not the incoming mail.
This next picture shows the actual location of the Medina mailbox on December 24, 2002. The privacy wall was built after the burglary/Laci's disappearance, and the mailbox moved to the side of the privacy wall.