My uncle managed to get into a nuclear power plant with the wrong clearance tag. He was working on two facilities and grabbed the wrong tag when leaving the office.

What he said was scariest is that anyone with access to a commercial printer and lamination machine could easily reproduce them too.

So many people come and go from your average facility. I mean you can get past most gates just by landing a job at the right landscaping company if security is that strict.

It also sounds like the target was in a shared office building, so they likely had minimal influence over security procedures.