Reyes was a Chief Petty Officer on board the U.S.S. Enterprise who ran a very tight ship with his personnel and regularly got them up to shape.
At some point, he began slipping members of his crew performance-enhancing drugs which left two of his men hospitalised despite them insisting that they had never taken any drugs whatsoever.
After a long investigation, NCIS were able to find proof of his actions and as such, arrested him.
Despite claiming to be fiercely protective of his men, Reyes knowingly put the life of his men at risk, simply for the sake of getting them up to speed as well as keeping his record intact.
Once he was exposed and arrested, Reyes showed no remorse for his actions, implying he was a psychopath or a sociopath.