You should, at a minimum, give the candidate the equivalent of an oral examination on the technical skills for two hours. With practice, you will be able to quickly cover what they know and quickly retract from what they don't know to mark out the boundary. Interviewees will respect this. I have several times heard interviewees say that the quality of the examination was one of their motivations for choosing a company. Good people want to be hired for their skills, not where they worked last or what school they went to or some other inessential characteristic.