For a month, the elderly black man - identified only as R.C. in court papers - insisted that the disfiguring injuries to his face were caused by a fall outside his Katy home.

He told no one, not even his daughter, that in fact he had been brutally attacked by a young white man with racist intentions who calmly drove up to him nearly two years ago, got out of his car and, after offering a seemingly friendly greeting, felled him with a single punch to the face.

In federal court on Friday, R.C.'s daughter, Donna McNeal, wept as she saw, for the first time, video footage of the attack on her father and explained why he kept silent.

"'If you grew up like I grew up, if a white kid, white man, white girl, spit on you, kicked you, punched you, you had to hold your head down and keep on going,'" McNeal explained to U.S. District Judge Gray Miller, recounting what her father told her.

The cellphone video, shot the week of Thanksgiving in 2013, was shown in court before 29-year-old Conrad Alvin Barrett was sentenced to 71 months in federal prison. He pleaded guilty in June to a federal hate crime charge for the attack on R.C.

Barrett has said he targeted the then-80-year-old to secure his place in the international "knockout game" phenomenon, which has hurt and sometimes killed people over the last two decades.

Other videos discovered by authorities on Barrett's phone during the investigation show him contemplating an attack while using racially derogatory remarks, including the "n-word."

In her testimony Friday, McNeal told the judge that her father ultimately told the truth when Fulshear police came looking for him after he was identified as the victim in the attack filmed on Barrett's phone.

While his daughter testified, R.C. watched from the gallery. McNeal said her father, who was outgoing and communicated "very well" before the attack, is now reclusive, "murmurs" when he speaks and has ongoing pain in his face.

Barrett, handcuffed and shackled, stumbled through apologies to the elderly man and his family as well as to his own parents and the judge.

He turned to look at his victim and said: "I apologize, Mr. R.C., and to your daughter. I'm sorry. I hope in the future I'll be able to help y'all in any way y'all need. Sorry."

Barrett called that day the worst of his life, which sparked an emphatic reaction from Assistant U.S. Attorney Ruben Perez.

"Your honor, that day was the worst day of R.C.'s life because of what this man did," the chief civil rights prosecutor for the Southern District of Texas said. "We did not have to research his position on race. ... He recorded his position on race - that's why we are here."

Dr. David Self, a psychiatrist hired by the defense, said bipolar disorder and drug use converged to "energize" Barrett's "willingness to pursue a goofy idea." He testified that the married man with family support who earned more than $100,000 a year diverged from his normal behavior.

"But for the presence of mental illness and substance abuse, this offense would not have occurred," Self testified, adding that Barrett had no history of "acts considered to be racist."

A federal hate crime charge carries a maximum punishment of 10 years in prison. Sentencing guidelines in Barrett's case called for no more that six years. Miller declined to vary downward from the calculated range and gave Barrett the most time that he could - one month shy of six years.

Miller also ordered Barrett to serve two years of supervised release after prison and pay $2,000 restitution to McNeal for wages lost while she cared for her father.

Barrett still faces an injury to elderly person charge in Fort Bend County.