IF BART police have an explanation for the fatal shooting of a 22-year-old Hayward man early New Year's Day, they need to start talking.

The amateur video of the incident seems to show an execution-style shooting of Oscar Grant III by an officer whom police refuse to identify, except to tell us that he has two years' experience on the job. The video shows Grant being shot in the back while lying face down on the Fruitvale station platform. It is a sickening scene.

Grant's family has already retained prominent civil rights attorney John Burris, who has talked to witnesses and reviewed three videos taken by onlookers. "What the witnesses said happened and what is on the videotapes are very much the same," Burris told reporters. "From that you get a real clear picture of what happened. From that you can easily determine that Mr. Grant was killed by this officer under circumstances that were woefully unjustified. It is without a doubt the most unconscionable shooting I have seen ever."

We have a similar reaction to the video. We want to keep an open mind. Perhaps the gun went off accidentally. Perhaps, as has been suggested, the officer mistakenly thought in the heat of the moment that he was firing a Taser stun gun. But now, five days after the incident, the police department's stonewalling is troubling.

Even more disturbing, it seems that, as of Monday, police had not yet interviewed the officer who fired the fatal shot. It would seem that police interested in getting the complete story would have talked by now to the man who pulled the trigger — to get his fresh recollection of the incident before he could concoct another explanation. It makes us wonder whether BART police want the unvarnished truth or would rather protect one of their own.

All we know is that there was a fight on a BART train within the first couple of hours of the new year. Officers were called to the station and several people, including Grant, were detained on the platform. We don't know if Grant was involved with the fight. We don't know how many witnesses there were on the train, but some took video of the incident.

It appears that some were handcuffed. But Burris says Grant was not: "Mr. Grant, at the time he was shot and killed, was in fact lying on his stomach with his back to two officers with one officer kneeling down at his neck and head area with a knee there and the other officer straddling over him. "... (Grant) did not have a weapon, he was not kicking. "... The officer for reasons that are the most shocking to me pulled out his weapon and within moments fired it directly into the back of Mr. Grant."

Burris plans to ask prosecutors to consider filing criminal charges against the officer. We are glad that Alameda County District Attorney Tom Orloff is conducting a parallel investigation. We hope it is rigorous. Indeed, we all want to know if this was an accidental shooting or a coldblooded murder.