No, it is likely they figured out what the thieves did from observing the crime scene. Not likely the thieves would want to carry many lbs of glass container, and they don't care nothin' 'bout this "strain" stuff. So they dumped it all into a bag and carried the bag out. Makes perfect sense. They could figure this out from seeing all the jars scattered about the room (assuming this is how it went). But in this case, according to the OP account, it was an "armed robbery" of two employees of the facility. The employees obviously witnessed the pouring into the bag. Doesn't mean they are part of the gang that did the robbery, although that is certainly something that should be considered, ie inside involvment. Anyways that is my take on the OP account.