Remember, BTK kept a little metal shed out back of the house that he kept locked. His daughter said no one was allowed in there. He told them it was his workshop, they always assumed he was back there working on carpentry, etc. projects. It's where he kept some tools he used in his crimes and the "souvenirs" he collected from his victims.
http://www.kansas.com/news/special-reports/btk/article1003734.html
I noticed DeAngelo also had a little shed in his back yard. He probably had some secret/private place where he kept some criminal tools over the years, in different homes he may have lived in. LE will find out.
I kind of wondered if he resorted to shoplifting for kicks, the same way he burglarized homes for years. He may have been doing it for years and it was just the first time he got caught.