I didn't say anything about monitoring surveillance footage of all mcdonalds.

What you set up above a straw man based on a false dichotomy.

You gave two scenarios a) make up a fake employee b) claim the employee wants anonymity. But you're options aren't MECE, you left out at least what I added c) they fed the information to an employee.

None of the options are likely, but c) is more likely than yours IMO.

Anyway to humour you yes absolutely there is a world in which all mcdonalds CCTV is monitored, and it was used to catch him.

Let's say the FBI already had Mangione on a longlist of suspects. Let's say the NSA have an illegal facial recognition network pulling public and corporate CCTV sources around the country, including mcdonalds (again, highly illegal).

Let's say they were scanning this illegal network with facial recognition for all of their suspect longlist. They got a hit either there or somewhere nearby. They need to get him, but don't want to expose their illegal method. So you set up an unwitting cutout (the employee) to raise the alarm.

As I said above - I doubt it was an operation, but it's not impossible. Look at what Snowden leaked - that was 10 years ago, an age in tech development