I think he was legal, but I just noticed this footnote:
47 Title 14 CFR 135.245 Second-in-Command qualifications, required a Second-in-Command hold at least a commercial pilot certificate with appropriate category and class ratings and an instrument rating. According to the FAA Form 8410-3 dated August 7, 2015, the accident SIC required retraining in the Lear 35A stall series.
To me (and again - I'm ignorant of this stuff), it would
appear that the companies definition of an SIC-0 would preclude putting someone with that designation into the right seat of a plane that legally requires a co-pilot. It would seem logical (and logic may have nothing to do with this) that an SIC-1 designation would be the minimum qualification for a plane that requires a co-pilot.
Does the Lear AFM list the duties that a co-pilot must be capable of performing, and does that list include being capable of flying the plane?