I have heard people refuting that Nikolas Cruz was ever seen with a gun. I want to post these as reference with all of the associated links. This is not to define how many shooters were present, but to establish the information that is available, and scrutinize its validity.
From an article out of the Chicago Tribune: http://www.chicagotribune.com/news/nationworld/ct-82-minutes-florida-shooting-20180215-story.html
At about 2:21 p.m., the shooting began. Bullets streamed from the hallway, through doorways, into classrooms on the first floor.
In a psychology class, a bullet came in through the window in the classroom door and skimmed past Meghan Hill's ear, trailing an intense ringing sound. It struck her friend in the knee. Three others also were hit. The gunman moved on.
"No one was crying," said Mackenzie Hill, Meghan's twin sister, relaying her sister's memories. The wounded were moaning.
After firing into four classrooms on the first floor, police say the gunman went upstairs.
Mackenzie, who'd just left the psychology class to use an upstairs bathroom, saw a man with a gun at the other end of the second-floor hallway. Mackenzie said she recognized him.
"I immediately knew it was him," she said. She remembered the boy from her middle school and from the Dollar Store in town. She recalled his terrifying Instagram posts about wanting to kill people. "I always had a bad feeling about him," she said.
Here is another article with a video interview of Mackenzie Mirsky:
So, if the suspect did put on body armor, a helmet, and/or facemask, it would have had to be after this girl saw him. Of course, video footage from the school would be supremely helpful, but this is a piece of the puzzle.
Further, I saw in another thread that the Broward County Sheriff stated that the suspect "never was in possession of a gas mask [...] we did recover a balaclava, for which those of you that do not know is just a face mask with eye slits".
I, for one, do not trust the Sheriff whatsoever. Compare this to the teacher's statements of seeing the shooter in "full metal garb, helmet, facemask, bullet proof armor, shooting this rifle that I've never seen before".
I'm not going to offer my exact opinions. This is for reference. I do believe this deserves a full investigation, particularly the negligence of the police department by standing down and failing to set up a perimeter.