Surveillance video from a Best Buy store shows the altercation between Librado Cena and William O’Brien on April 16, 2013. The second clip shows Cena interrogated by Fairfax City Police Detective Michael Boone on April 18, 2013. (Fairfax City Police)

Robin Remsburg told a jury that she waited days for her husband to regain consciousness after he was punched during a road rage incident in April. He endured surgery and painful tests, but his eyes finally fluttered open.

She expected the man she loved to gaze back at her, but instead she saw a “horrible blank stare.” William O’Brien’s brain had been damaged beyond repair by the blow. She had him removed from life support soon after.

“I have been a nurse for 35 years and seen tragedy,” Remsburg told a packed courtroom. “I knew [my patients] suffered, but I didn’t know the depth of that suffering. I do know now.”

Librado Cena, 58, was sentenced to three months in jail at the hearing in Fairfax County Circuit Court on Wednesday for delivering the single punch that led to the 63-year-old man’s improbable death.

Cena was convicted a day earlier of misdemeanor assault in the case, but Remsburg told the courtroom at the sentencing hearing that she felt little solace. She couldn’t understand why Cena had faced such a minor charge.

“I believe the legal system has failed my husband and family,” Remsburg testified. “He should be on trial for homicide.”

Cena and O’Brien, both of Fairfax City, encountered each other on the roads near Fair City Mall on the morning of April 16. Cena testified during the trial that O’Brien honked at him “incessantly” at a number of lights.

Cena was irked, so he followed O’Brien into the mall’s parking lot to yell at him, he told jurors. Surveillance footage shows Cena running up behind O’Brien as he trudged across the parking lot. A fight ensued.

Prosecutors said Cena instigated the melee, but Cena contended it was O’Brien who was the aggressor. Either way, Cena testified that he punched O’Brien in the face just once and the pair parted.

The incident initially appeared minor, and O’Brien and Cena continued on with errands. But O’Brien called 911 from his home a couple of hours later complaining of a headache that was about to make his head “blow off.” He collapsed and died 10 days later.

A medical expert testified during the trial that O’Brien probably would not have died except he was on the blood thinner Pradaxa, which kept blood in his brain from clotting. Pressure built up in his cranium, causing brain damage.

Cena, a former director of religious education at a Fairfax church, was initially charged with aggravated malicious wounding, a felony. But prosecutors later dropped that charge, saying it didn’t fit the circumstances of the case. A grand jury indicted him for misdemeanor assault and battery.

Kelly Sprissler, Cena’s attorney, argued during the sentencing hearing that he should not be judged by the “worst few seconds” of his life. “There is a lot of good here,” Sprissler said of Cena.

O’Brien, an Army veteran and retired mortgage industry worker, died two months before the birth of the grandson named after him.

“There is absolutely nothing that can make up for the senseless loss of my father . . . and knowing my son will never know him,” Kelly O’Brien testified.

A judge will formally impose Cena’s sentence May 9. The judge can decrease the jury’s punishment, but not increase it.

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