How well guarded are zoos after they close at night?

Let’s just say I’m an “animal lover” who helps wealthy individuals acquire “collectables.” I particularly like large African animals such as rhinoceroses, leopards, giraffes, gorillas, and especially lions. Unfortunately, I’m a wanted fugitive in most African countries, and North American animals are no were near as “interesting” to my clients as African specimens are. I spent the past few days touring zoos, treasure troves for animal lovers like myself. I was impressed by the white lions held at the Cincinnati Zoo. They had absolutely stunning fur, the kind of thing my clients would love see. I was wondering how difficult it would be to sneak into the zoo with my equipment, conduct my business and leave without anyone noticing. Have any other “animal lovers” tried that before?