I THINK that you do NOT 'know' any such thing at all; but merely BELIEVE what you have been taught by the religious organization based in Salt Lake City.
The FACTS are that only ONE man was ever found guilty of ANY crime associated with MMM: John Doyle Lee.
Folks can GOOGLE® his name and read all KINDS of things about him; but NO WHERE will they find out how he was able to kill all those people by himself.
He could NOT have been able to shoot that accurately or reload that rapidly to get it done!
Aside from a damning statement by one of the local Indian chiefs, to absolve Brigham Young of responsibility for the MMM is absurd for a couple of reasons.
First, in Utah at that time, you couldn’t blow your nose without Young’s permission. It was like Iraq under Saddam. Secondly, John D. Lee was very close to Young, and had even been sealed to him, essentially as an adopted son. It’s therefore ridiculous to suggest that his actions were that of some kind of loose cannon.