I really haven't read anything about this story, so I won't comment on this particular case. In general though, I don't think anyone should be executed based on witness account alone. If there is other evidence fine, but not just because other people say they saw it.
Lots of people swore they had seen women perform evil witchery too.
**p.s. It is my belief that any violent career criminal should be shot where they stand...if this guy fits that bill, so be it.
This took place in a Burger King parking lot, in front of a couple of dozen people, after Davis and his buddy had attracted everybody's attention by pistol-whipping a homeless man who was screaming for help. The eyewitnesses did not know each other, but all of them independently described to a 't' Davis's clothing and appearance, and picked him out of a lineup. A couple of them knew him by name. When you get consistent, independent statements, that's a pretty good indication of truthfulness. See Susanna and the Elders (Daniel ch. 13).
Forensic evidence: Davis just a short time before shot somebody at a party. The shells recovered from that shooting scene matched the shells recovered from the shooting of the police officer. The pistol was never found because Davis threw it away (and told a friend he threw it away).
More forensic evidence: police found the officer's DNA on Davis's bloody clothing, which he had discarded at his mother's house. That evidence was not introduced at trial because his mama lied after the fact and said she had not given permission to search the house. But there it is.
Additional evidence: Davis admitted to two friends that he had shot the police officer because he got a good look at his face and could identify him. That doesn't include the jailhouse rat who retracted his not-very-believable statement (the details didn't match up with any of the eyewitness accounts).
Finally, the officer identified Davis over the radio before he was murdered. Identification from beyond the grave good enough for you?
My wife's ancestors came over on the Mayflower and has done extensive genealogical investigation and on the witch executions in Mass. She is convinced that many of these executions were carried out for political reasons where women received inheritances and others wanted it. One of her relatives with wealth was executed as a witch. We should never underestimate the evil and power of politics and the willingness of those without ethics and with ambition to do whatever it takes to advance their own interests. I agree if one is actually caught in the act of a crime then kill them outright, otherwise capital punishment needs to be applied only if the crime is nailed down 100% by facts, not just witnesses.