Road Rage Altercation Leaves One Man Dead

The defense argues that the blow to motorist's head was not what killed him.
3:00 | 02/25/14

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Transcript for Road Rage Altercation Leaves One Man Dead
We'll switch gears to a road rage incident that left one man dead after allegedly being hit on the head of the whole altercation caught on camera. A key question, who threw the first punch. ABC's Mara schiavocampo is here with the latest 0en that. Ma Mara. Reporter: It's a case so unusual at first prosecutors were unsure what the charges should be when it was revealed the victim didn't die as a result of the fight alone but also because of a blood thinning medication he was taking. Take a close look at this surveillance video showing two motorists driven to violence in a parking lot in Fairfax, Virginia. This morning, 58-year-old lee senna is in court facing misdemeanor assault and battery charges after getting into this fistfight with 63-year-old William o'brien last April. All because senna said o'brien honked at him too many times. Prosecutors say the fight resulted in o'brien's death. I wanted to yell at him, okay, and vent and he attacked me. Reporter: The fight lasted less than one minute and both parties walked away, but hours later o'brien called 911 telling the dispatcher, quote, I have a headache that is about to make my head blow off. Then ten days later o'brien, a father of two, died from a brain injury made worse by a blood shinning medication he had been taking. Senna was arrested after o'brien died. He was brought back to the station, interviewed and subsequently charged. Reporter: This video released of his interrogation is shedding new light on the confrontation showing the moment senna, a former Sunday school teacher first learns o'brien has been hospitalized because of the fight. From me hitting him. Yes. You're kidding me. Reporter: Senna admits following o'brien into the parking lot but says it was only to confront him verbally. I am backing up the whole time. The whole time. He was the one who was aggressive. I only struck him after he hit me. After he hit me. Have police look at the tapes. Please. You're using them to condemn me. At least look at them to see if I'm telling the truth. Reporter: Prosecutors say it's not the truth and senna threw the first punch. They'll have to figure out who was the initial aggressor, the defendant who went up to the victim and said some things verbally or was it the victim who an eyewitness claims was the physical aggressor coming at the defendant. Now, he did initially face more serious charges but prosecutors dropped them saying they didn't fit the circumstances. The maximum penalty for those charges is 12 months in jail. He has pleaded not guilty but he has admitted he should not have followed that man in the parking lot. A lot of eyes in this case. The next story began as a

This transcript has been automatically generated and may not be 100% accurate.

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