Sen. Bill Nelson said Wednesday that the alleged shooter in the attack that killed 17 people at a South Florida high school "wore a gas mask and had smoke grenades."
"He went and set off the fire alarm, so the kids would come pouring out of the classrooms into the hall," the Florida Democrat told Jim Sciutto on CNN about the suspect, identified by police as Nikolas Cruz, 19.
"There, the carnage began."
FBI officials did not tell Nelson whether the suspect used the grenades.
"I assume that's why he had the gas mask on," he said.
Broward County Sheriff Scott Israel told reporters Cruz was arrested by local police about two hours after he opened fire at Marjory Stoneman Douglas High School in Parkland, Florida, about 2:30 p.m. ET.
Cruz, whom Israel said was expelled from the school last year for disciplinary reasons, was arrested without incident in a nearby city.
The suspect used an AR-15 assault-style rifle and had multiple magazines, the sheriff said.
"How many more of these do we have to go through?" asked Nelson, who was first elected to the Senate in 2000. "When is enough enough?
"It's not going to change until the American people say we have had enough."