If, as the man who took the video stated, there was a fight on the ground and the man assaulted the officer and tried to take his weapon, (taser or otherwise), the officer could make the case that the standard of "committed a crime involving the infliction or threatened infliction of serious physical harm, deadly force may be used if necessary to prevent escape" had been met.
If you watch the video carefully, the shooting lasted only 2 1/2 seconds and there was a pause before the last shot and the man was clearly still running before the final shot took him down. Have to keep saying this: not defending at this point, just pointing out the law and the facts we know so far. To say this was simply a traffic stop and the man ran so he was shot for back child support is BS. People should be very careful. I remember a number of freepers defending Trayvon Martin and Mike Brown before all the facts were known.
Even if this DOJ opinion is correct the officer will find it difficult to meet that requirement.
Then the police made a mistake when they watched the video and charged him with murder.