Actually, it is not likely that Reid killed Soapy Smith. Instead, it was probably a railroad carpenter named Jesse Murphy.
The version of events that prevailed immediately after the incident was that Smith and Reid both shot and wounded each other. Smith was down and either dropped his rifle or Murphy grabbed it from Smith and, in either event, Murphy fatally shot Smith. Smith probably said, "For God's sake don't shoot," when Murphy pointed the gun at him. That version of events prevailed until someone went up to White Pass to report the incident to Sam Steele of the North-West Mounted Police. Steele told the person that he (Steele) had no jurisdiction over the matter. Based on subsequent events, my opinion is that Steele also told this person that what Murphy did would not be excused as self defense. For self defense to apply, you need to be threatened with death or severe bodily injury at the moment you pull the trigger. Once any danger is gone, this defense vanishes. Since Smith no longer had his gun, Murphy could no longer claim self defense when he shot Smith. In later years, Steele said that Murphy was probably the shooter.
As soon as this person got back to Skagway with the info that Steele had given him, the prevailing story miraculously changed. Suddenly, in the new version, it was now the other dead guy (Reid) who shot Smith - not Murphy. Also miraculously, the guns involved disappeared - probably to the bottom of Skagway harbor. That disappearance was a little too convenient! Now, nobody could inspect the guns to determine who fired the fatal shot. If Reid's gun had killed Smith, they would have kept the guns to back up their modified story. The only reason to throw the guns into the harbor was to cover up what actually happened.
Robert