Florida high school gunman was reportedly equipped with smoke grenades, tried blending in with students during escape

Wilfredo Lee/AP

A law enforcement officer informs family members to step back, February 14, 2018, in Parkland, Florida.

• Nikolas Cruz, the 19-year-old gunman in the high school shooting that killed at least 17 people on Wednesday, had reportedly done "enormous preparation" for the act.
• Cruz is believed to have been equipped with a gas mask and smoke grenades.
• He reportedly pulled the school's fire alarm in the hope of causing massive casualties.

A lawmaker said the Florida high school gunman that killed at least 17 people on Wednesday had done "enormous preparation" for the act and was equipped with a gas mask and smoke grenades.

Sen. Bill Nelson of Florida said law enforcement officials had briefed him on 19-year-old Nikolas Cruz, the shooter who carried out the attack on Marjory Stoneman Douglas High School in Parkland, Florida.

Cruz is believed to have intentionally set off fire alarms "so the kids would come pouring out of the classrooms into the hall," Nelson said on CNN.

"There the carnage began," Nelson said.

Cruz, a former student at the high school, was taken into custody without incident and was cooperating with law enforcement officials. He is believed to have been equipped with an AR-15 and "countless magazines," the Broward Sheriff's Office reportedly said to ABC News.

After the shooting, Cruz reportedly tried to escape by blending in with other fleeing students, law enforcement sources and eyewitnesses said to ABC News.

The investigation is being led by the FBI, according to Nelson.

"It is clear attack was designed & executed to maximize loss of life," Sen. Marco Rubio of Florida said on Twitter.

The school enrolled 3,208 students between grades nine and 12, according to the Sun-Sentinel.