They spent the weekend rafting the Truckee River and reminiscing about their years together, a group of childhood friends who had grown up in Southern California and had flown to Reno, Nev., to celebrate another of life’s milestones.

The men in their early 30s had come for a bachelor party weekend, and their guard might have been higher amid the casino bustle the night before. But in the brisk Monday morning air, during a casino’s quietest hours, the friends were simply trying to catch a short Uber ride to the airport.

That’s when a man walked up, seemingly out of nowhere, and shot several of them in what the police described as a random attack.

Two of the friends died. Two people were severely injured, and a third had minor injuries. Another man, driving through the parking lot, was shot dead at random shortly thereafter, the authorities said.

It was an immensely tragic end to a weekend that had been intended to celebrate the start of a new marriage.

“I’ve seen these guys growing up,” said Scott Juceam, the uncle of one of the men who were shot and hospitalized. “They’re very close — they’ve known each other most of their lives. It’s just terrible.”