It seems maybe he was telepathically influencing everyone to act stupidly and to never raise basic doubts. Barry could have taken a leaf out of eobard and taken the stand as flash although the question of masked testimony being invalid does raise head. perhaps the judge could have allowed it as tgeir were exceptional cirumstances if the flashs testimony could prove a officer of law was innocent and was framed by one of flash meta villains. If only the autopsy had revealed if he is a metahuman but I think devoe would have covered that angle somehow though the show doesn't bother showing the autopsy report at all.