
Many commenters under the linked video saying the police here were stupid. Wondering what the pros here think (see body text for more context)
They stop a woman for driving without a tire on one wheel. There happens to be a dead body in her trunk. But they don't feel they have probable cause to open the trunk. And she explains some things they are seeing and smelling about the car with "innocent" explanations. They let her leave to go home but keep the car. After she leaves, without change that I can see in what they see in the car, they decide they do have probable cause to open the trunk, and find the body.
I suppose one might wonder why they didn't figure out they had probable cause while she was still there. I could imagine that an officer encounters many different situations and it could be hard to figure out what to do in the pressure of the moment. Also, you can change your mind, they may have thought they didn't have probable cause and then with more time and discussion (after she happened to leave) decided they did.