George Parnham, Barrett's attorney, had argued that the Katy man has been diagnosed with bipolar disorder and was off his medication when he used his cellphone to record video of the apparently random attack.
Prosecutors say the attack happened Nov. 24 in Katy, but it wasn't until 12 days later that authorities connected it to the cellphone video and arrested Barrett.
According to prosecutors, the attack happened on November 24 in Katy, Texas, but it wasn't until 12 days later that authorities connected the attack to the cellphone video of it.
Authorities learned of the case because Barrett allegedly showed the video on the night of the attack to an off-duty arson investigator he had just met at a restaurant in nearby Folshear.
According to the criminal complaint, Barrett asked the off-duty investigator and the woman with the investigator if they knew about the knockout game.
He told them he played earlier that day, then showed them the video, prosecutors allege.
The investigator then flagged down a uniformed officer across the street and led him to Barrett.
The attack video doesn't show Barrett's face, but investigators matched his voice to the voice in the video and the couple at the restaurant told investigators that Barrett was wearing the same shorts and shoes at the person who shot the video.
According to prosecutors, the video shows Barrett approach the victim and ask, 'How's it going, man?'
A 'loud smack' is then heard, the victim falls to the ground, Barrett laughs and says, 'Knockout'. The assailant then flees in his vehicle.
The victim lost three teeth and needed surgery to repair his jaw, which had been broken in two places. He was hospitalized for more than four days, authorities said.
*Pictured above is Conrad Barrett and the 79-year-old victim.