Las Vegas Cop Killers Were Husband-Wife Team
LAS VEGAS, June 9, 2014— -- The couple who ambushed two Las Vegas cops and killed a civilian in a nearby Walmart store were a husband and wife team ...
https://abcnews.go.com/US/las-vegas-...ry?id=24052877
Not exactly an example of what the OP is looking for, but the private citizen went to engage the husband and the wife shot him as he passed by her.