Not one Morton-Thiokol engineer signed off on that launch. Not a single one. It was approved by (presumably non-technical) managers.
Richard Feynman was on the Challenger investigation team.
He had a lot to say about it.
http://www.feynman.com/science/the-challenger-disaster/
https://www.discovermagazine.com/the-sciences/the-feynman-file