The point is, you have to prove to a jury that not only specific items were stolen, but that anyone holding those, or even reselling them, had knowledge they were stolen. I've literally seen instances where individuals holding entire warehouses of hot tools got off the hook by playing dumb before a dumb jury. You need things like specific serial numbers matched on recorded receipts to the items under possession. Locally, it's amazing what the police detectives know about theft rings and their associates. But they're very reluctant to move with an arrest unless they got the culprits neck deep in poo-poo, and are 99% certain they can obtain an actual jury conviction.
In our case, grab n' run shoplifters, once they got off the property, the company parking lot, through the gate, then it was illegal to stop them. Didn't matter how many thousand of dollars they ran out with, or lack of a receipt. At that point, a police investigation was required, and that was a long long line indeed.
En-route truck heists, or missing pallets of equipment, happened at least twice a year. That's what mfg and insurance detectives were for. Never had to make a claim ourselves. Those guys did it right, and did it fast. A few phone calls, and the missing stuff turned up a week or two later, and the carrier was never trusted again. But being a major distributor, we had a lot of clout. Smaller dealers didn't, or just didn't know the ropes.
Armed robberies? Well, I remember that kind of thing more from back early on when I worked in the south end of SF. But I was a helluva lot more afraid of the security guard himself pulling a gun and doing something wild. Like many security guards who couldn't find better work, he was an ex-con, and even went around bragging what his own big heist would be someday.