drugs. tough, new auto emission standards about to be announced, but will they push more americans to go electric a big upside of artificial intelligence, detecting cancer much earlier, and predicting when it might strike and the young, bold athletes sharing their culture and superstar tony hawk. announcer: this is nbc nightly news with lester holt welcome. once again, in the tragic aftermath of a mass shooting, we re getting a person look at pol risking their own lives to stop an active shooter late this afternoon, louisville police releasing body cam video of officers rushing to a downtown bank yesterday, immediately coming under fire from a bank employee he was armed with an ar-15 assault-style rifle, carrying out a murderous rampage, fatally shooting five people the gunman killed by police tonight one of those officers, who rushed to stop the gunman, a rookie, just days on the streets, remains in critical condition, and tonight there is a deeper understanding