We actually do know exactly when the main concrete slab (that was cut by LE) was poured. The inspection record shows that last items to be inspected before a slab pour of that type........the "Insulation Under Slab" and "Plumbing - In Floor Tube" passed on Monday May 11, 2020. This would be the morning after Suzanne's disappearance. Normally there are two to four days after inspection after a pour, to ensure that there were no post-inspection changes and that everything went well and the dry, finished slab will conform to code. The same inspector did return on Thursday May 14, 2020 and noted some sort of failure in the forming of a future footings pour......."Caissons/Piers". This is usually something that was already set, but got messed up by the work activity of the Monday pour, like a collapsed trench wall. Whatever it was, the timing of the inspection strongly indicates that the concrete pour was begun on Monday. There is a lot of concrete there, requiring the loads of several concrete trucks. It's quite possible that the pour spanned over into Tuesday morning. A different inspector returned on May 15th to pass on the remediation of that Caissons/Piers problem, but there was not a subsequent post-pour inspection, which might indicate that the work had been suspended at that time.
The ground penetrating radar that LE used to narrow their search is only useful to a soil depth of 2 feet below concrete but will detect both objects and voids. The Channel 9 News video taken after the search clearly shows the hole cut by LE, and shows that the LE excavation was at least two feet deep. There is only one conclusion possible, which is that they were looking for something that was buried BEFORE the insulation and plumbing that was inspected on Monday May 11th were installed. This does not match the timeline of SM's disappearance.
My personal opinion is that the timing of the work immediately prior to the pour and the depth of the pour tend to indicate that LE was looking for something that BLM could not have done in the routine course of his landscaping trade. My guess is that LE initiated the search on solid information from an informant (or informants) in a position to know, and may well have been been an observation of the suspicious activities of someone other than BLM. The decision to search the site may have come as early as five days after the report of her disappearance, and if so, probably had no direct connection to discovery the other searches.
Like everything connected with this case, what we don't know greatly exceeds what we do know. IMO
Building Department Permit Detail