Matthew Murray was armed with hundreds of rounds, ready to kill as many in the New Life Church sanctuary as he could. He had already killed two people in Arvada at a missionary training school, and had shot a family and another woman, killing young two sisters in the New Life parking lot on his way into the church.
Murray entered the sanctuary and opened fire, shooting one person in the arm.
Before he could shoot any more, he was shot and badly wounded by Jean Assam, a security guard and church member carrying a concealed weapon. After Assam shot him several times, Murray shot and killed himself.
Jean Assam saved the lived of at least 100 people that day because she was armed in a place the gunman didn't expect an armed person to be.
The Tacoma Mall (Washington State, 2005, 6 wounded) shooting was stopped after the shooter was confronted by a citizen with a pistol. Although the citizen did not fire but was shot and paralyzed, the shooter retreated into a store with no more shots fired.
The mall shooting in Utah (2007??) was in part stopped by an off-duty cop with his family IIRC.