Who killed Joseph Smith podcast

Yesterday I stumbled upon the Who Killed Joseph Smith podcast on YouTube. I watched the two part “Who Killed Joseph Smith?” documentary that was created. The director explores several different theories about the murders and then comes up with the theory that Willard Richards and John Taylor actually committed the murders and not the “mob”. He was so adamant in his position that it got him excommunicated from the church. But in watching it I began to think, this theory is very plausible because why weren’t Richards and Taylor killed too. If these “Mormons” were such a threat wouldn’t they just wipe all of them out? I actually believe that it was an inside job. Has anyone else ever thought about this?