FORT LAUDERDALE, Fla.—The suspect in the 2018 killing of 17 people at a Florida high school is finally going on trial—but not for the slayings. Jury selection begins Monday on charges Nikolas Cruz attacked a Broward County jail guard nine months after the Feb. 14, 2018, shootings at Marjory Stoneman Douglas High School in Parkland. Cruz, a former Stoneman Douglas student, brawled with Sgt. Raymond Beltran after being jailed on charges of killing 14 students and three staff members and wounding 17 others. No date has been set for the murder trial, which has been delayed by the pandemic and arguments over witnesses and evidence. It may start in the next few months. “The accused murderer who took our children’s lives is clearly violent and took that out on a guard. He needs to face the justice system for that,” said Tony Montalto, president of Stand With Parkland, a group …