Ha ha yeah, it's definitely tempting to speculate. Exactly what I'm doing. I am on True Crime Brain right now, please help me. But I'm refraining from accusing zoo employees or anyone specific. Public speculation on high profile crimes can do a lot of damage to innocent peoples' lives, I don't want to contribute to that.
If the zoo has reason to believe the tamarins were taken, I'm leaning towards profit motive, personally. Leopard exhibit was cut open but they weren't able to catch the leopard. Monkey exhibit was cut open, but something prevented them from stealing. (maybe the monkeys hid or climbed beyond reach? Or the thieves realized that someone was nearby?) Tried to steal vulture, but it resisted and possibly got aggressive and was killed in the struggle. Finally, they had a successful theft with the tamarins.
Profit motive becomes more plausible if the animals are especially valuable. I'm not super familiar with the exotic pet market, so correct me if I'm wrong on these things. I really doubt that endangered vultures are common on the exotic pet market, I don't think it's even legal to have them as pets in the first place. (in the US) So, could potentially be valuable if they had a buyer. Clouded leopards, as far as I've seen, don't seem to be common on the exotic pet market. Like, I don't think I've ever seen someone have one as a pet, and I don't see listings online for cubs, I don't even see them at sanctuaries for exotic pets. So they could be potentially be valuable. Small primates can be a little harder to pin down, but it doesn't seem like langurs and emperor tamarins are common? At least, I'm not seeing anything on a quick search. Someone who knows more about the exotic pet market could provide more valuable input.