I'm thinking that they asked general questions concerning his use of a tranquilizer gun and the materials that he uses. Since that line of questioning might have caught him off guard, he didn't know why they were asking these questions and what they may have found. That might be why he confessed to disposing of the tranquilizer material.
I think that he made sure to split up the damning evidence into different bags and put into different dumpsters. So, if one thing was found, all wouldn't be found.
As I am reading about what he has done, it seems to me that he has used bits from several criminals. He stripped the bedding like Chris Watts. He got rid of Suzanne's possessions like Scott Peterson. He disposed of crime evidence like Dulos and Frazee. He disposed of the body like Josh Powell.
I think that there was no way that Barry was letting Suzanne and her money go. Just the thought of her enjoying her life with another man and using her inheritance money as part of her happiness probably enraged him. He'd rather see her dead.
Of course, he doesn't feel guilty. He blames her. He's the victim. That's how all narcissists think. She made him do it.
JMO.