In the context of William's investigation into the missing person case, a secondary source is typically one that provides information that is not directly from someone who experienced or observed the event but rather comes from someone who has heard about or recorded the event.
Among the options provided:
A. Mother of missing person interview (on record - Police Station on February 13) - This is a primary source, as it's coming directly from the mother who experienced the situation.
B. Possible missing person security video outside payphone on February 13 - This is also a primary source, as it is a direct recording of an event.
C. Restaurant worker interview (on record at deli beside payphone on February 13) - This is a primary source as well, as it comes from a witness who observed the argument.
D. Tele Service phone records of the missing person's home on February 13 - This is a primary source too, as it is a direct record of the call that was made.
Since all of the options provided are primary sources, none of these can be classified as a secondary source based on the definitions typically used in investigative contexts. However, if one had to consider a secondary source, it would be a source that offers commentary, analysis, or discussion about these primary sources rather than being a direct account or record of events.
In conclusion, since none of the options listed pertains to a secondary source, it appears that all the listed sources are primary.