The Justice Department's decision to charge a white man with a federal hate crime for a "knockout game"-style attack against a black victim has raised questions about why the administration waited until now to speak up on cases that, for months, largely have involved white victims.

Federal prosecutors presented a detailed set of evidence Thursday in charging Katy, Texas, man Conrad Alvin Barrett, 27, with a hate crime. He allegedly shot video of himself using racial slurs, stating his intent to hit a black person in order to receive national media attention and, in the end, punching a 79-year-old black man.

The attack was serious. 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.

Barrett’s attorney George Parnham told Fox News on Friday that Barrett has been diagnosed as bipolar and has battled alcoholism, going “in and out of rehab,” since the early 2000s.

Parnham said he wasn’t suggesting those two things, in combination, were responsible for Barrett’s mindset on the day in question, but said those factors “cannot be discounted when making determinations about the decision-making.”

But some questioned why the federal government just now was getting involved and whether a double standard was at play, considering that in many prior cases, the race of the suspect and victim was reversed.

A number of those cases probably would not qualify as a hate crime -- prosecutors would need to have evidence that the victim was targeted because of race or religion. But several apparent victims of a rash of attacks in New York were Jewish. Police originally said an alleged assailant in one attack against an Orthodox Jew was charged with a hate crime in November, but that turned out not to be the case.

Defense attorney Bernie Grimm told Fox News that the latest charges appear to be the Justice Department "saber-rattling" because "they want the country to think that they are on the front edge of this knockout phenomena."

Former assistant U.S. attorney Fred Tecce said it appears the suspect here is a "terrible guy." But he, too, questioned the role of federal prosecutors.

"We have had a ton of these knockout cases," he said. "Part of your role as prosecutors and part of the role of the Justice Department is to send a message to the public that ... the law applies to everyone."

He added: "Why is this the first knockout case that the DOJ has decided to render an indictment on?"

In some cases, the Justice Department might have no jurisdiction at all. There is no generic federal assault charge, though charges could apply if the victim is a government official or law enforcement officer. Without the hate-crime element, assaults typically are charged in a state court.

Legal experts said the feds got involved here for two reasons: First, to ensure a stiffer sentence in the event of conviction, and second, to reassure the public that law enforcement has a handle on the sickening spate of crimes.

According to prosecutors, the video of the attack 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.

Investigators retrieved other videos from Barrett's phone, including some in which he uses racial epithets and talks about trying to work up the courage to play the knockout game, the complaint states. In one, Barrett says: "That plan is to see if I were to hit a black person, would this be nationally televised?"

U.S. Attorney Kenneth Magidson said Thursday that such crimes won't be tolerated.

"Evidence of hate crimes will be vigorously investigated and prosecuted with the assistance of all our partners to the fullest extent of the law," Magidson said.

Defense attorney Ted Williams defended the Justice Department's involvement here.

"[Barrett] also during the course used the 'n' word. There may be those that would say the requisite intent for the national hate crime is not there but I do believe that this would be an excellent test case," he said.

A conviction under the federal hate crimes statute would mean a maximum 10 years in prison and a $250,000 fine.

Fox News' James Rosen and The Associated Press contributed to this report.