Go back to step 1, and you might succeed.

What is the goal of your interview? What skills are you looking to detect? What problems do you want to detect?

Then design your interview to achieve your goals. Check to see that your questions and techniques all support your goals.

I was a senior software engineer, when a Sr. Director asked me to take his interview slot. I asked him what I was supposed to cover. He told me. I sat down for a day or two... and thought through how to achieve those goals.

And I know I did it right, because I saw things others didn't. I filled in my slot in the whole interview design the company had.