Or could one of these have been used?
"In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of intravenous therapy or for blood sampling of venous blood. In healthcare, this procedure is performed by medical laboratory scientists, medical practitioners, some EMTs, paramedics, phlebotomists, dialysis technicians, and other nursing staff."
"The test tubes in which blood is collected may contain one or more of several additives. In general, tests requiring whole blood call for blood samples collected in test tubes
containing some form of the anticoagulant EDTA. EDTA chelates calcium to prevent clotting. EDTA is preferred for hematology tests
because it does minimum damage to cell morphology." (BBM)
https://en.m.wikipedia.org/wiki/Venipuncture
If they haven't yet, HCSO should test any remaining sample collected at the shop for these types of substances, IMO.