I have the impression that the first searches of 2610 Oxford Rd began around 12/12/16. Unfortunately, I cannot find the link for this information. I do not believe the house was searched the first week DS was missing. After the 12/22/16 search, the neighbor that lives directly across the street said:
"There was a couple of days in a row they were out here and they weren't out here for a while and then they were here the other night"
http://bit.ly/2iX3DYF
As the attorney poster said in a previous thread, the initial search may have been a warrantless search based on exigent circumstances. If LE had a warrant for the first flurry of searches, they could have relied on electronic evidence, surveillance video and info from witnesses (in the press conference they said they had gotten a lot of calls from people).
They certainly got DS' cell records quickly. Likely her computer and other associated electronic evidence (from her emails, SM accounts). I am guessing that they may have gotten info from 3rd parties that pointed them towards the SG. The moment he looked like a possibility, well before they had probable cause, I'm sure LE submitted preservation requests to save all cell & electronic evidence flowing from the SG- both retroactively and prospectively to save it until they had probable cause for a warrant. Perhaps the SGs wife gave LE access to a joint cell plan records or a shared computer.
I expect LE secured lots of surveillance video. Even though they didn't have video of the MetLife parking lot, they may have found other video useful in documenting probable cause. Perhaps video showing the SG at the Southfield MetLife complex before 5PM. Maybe there was video that demonstrated the SG was not at locations he was supposed to be during the key time period.
They may have had info related to SG's job, perhaps even gps data from a company vehicle or other equipment. Maybe he had a job related computer that the job gave LE access to. We do not know that the SG was fired in Oct, just that he stopped working at the Southfield location.
Although LE said they didn't see anything obviously amiss in DS' car on Sat night when they first saw it, they may have found evidence linked to the SG once it was carefully examined.
There must be other sources of evidence that I am not thinking of but I think third parties and DS' cell were critical.