Early in the morning on New Year’s Day, a man drove a truck into a crowd of people celebrating on Bourbon Street in New Orleans. In the hours since, law enforcement has discovered key details that point to a possible motive, including an Islamic State flag in the attacker’s car. Guest host Rachel Siegel and Justice Department reporter Perry Stein break down what we know about the terrorist attack in New Orleans.We also talk about the investigation into a possible attack in Las Vegas with some eerie similarities, though no known connection.  Today’s show was produced by Ariel Plotnick with help from Emma Talkoff and Elana Gordon. It was edited by Maggie Penman with help from Monica Campbell and Reena Flores. It was mixed by Sam Bair.Subscribe to The Washington Post here.