[sidlls]

Have them talk about the problems they solved at their current and previous employers, and get to some technical depth while doing so.

This doesn't mean asking him to implement some CS algorithm from scratch on the board or doing a Big-O analysis.

It means asking him about the specific methods and how/why they worked and going into some depth. His former employers' "company secrets" aren't a good excuse for hedging here, either: with few exceptions he should be able to use a contrived, but representative system, data, etc. to explain if he truly contributed to the solution.