Let me say that the Tech Interview process that most major companies use is screwed up.
When your company recruiter has to send your candidate a book on how to interview, it is messed up. What end up happening is the even the creators of popular open source software can’t pass the interview. https://twitter.com/mxcl/status/608682016205344768
Would a company in this day and age, design software that required a big user manual to use?
Go back to the old style interview where you ask questions on their resume and experience. Don’t ask questions on red black trees, if your the job does not involve them.
And check for a culture fit and if the candidate meets the requirements then hire. Don’t hire superstars and make them fix web forms. It always ends in disaster.