my key wouldn't come out and it wont start it says security theft on the screen im trying to figure out how to fix it with out taking it to the cts shop

Hey the ecm is usually your issue whenever the key is stuck and security theft system is engaged. I’ve worked on multiple cadillac cts’s with this issue. I have ecm’s for your vehicle starting as low as 250. They’re easy to replace just check out any youtube tutorial on these things the difficulty level of changing these things are 1/10 super easy for a beginner who has no knowledge of fixing an automobile.

They have three holes I can't remember which one but get a little strew driver push in on the one closest to you and it will let you turn the key back and it will come out it's just in theft mode

I'm sorry under the steering column