I used to fiddle with all sorts of chemicals. Once, I decided that it would be great to kill the mice in the cold air shafts of the house with Bromine. It worked perfectly, and wiped out whole families of rodents. The problem surfaced three days later, when the deceased mice began to decay. The whole house stank horribly.My mother was not impressed.
Eventually, we retrieved the mice using a bag of sand and a roller skate. The roller skate pulled a cord from one part of the shaft to another, and by pulling a sandbag with the cords, we got the mice to where they could be retrieved. I think we did in about 23 mice.