Who said he is a mujahid?
Despite his motives, Muslims all over the world are celebrating and they would’ve been happy even if a kafir did this. Thirteen less kuffar who would otherwise quite possibly have raped your Muslim sisters and/or killed them and other Muslims.
I think there is a difference of opinion on whether his job as a psychiatrist was haram.
Mubin Shaikh speculates on the monsters Mohammedivation.
In other news: Pass the cream cheese Elmo.