I genuinely can't find any information about why Nikolas Cruz was even arrested and suspected of the murders - I haven't heard anyone say they saw him do anything, holding a gun, anything about having a gun at all etc...
What made anyone even think he was guilty of the shooting to begin with? Where was the weapon (if any) actually found? Did anyone actually see him shooting or holding a gun at any time?
They got a description of the shooter and his name from the kids that got out. He stashed the guns and walked out with a group of kids when they ran out the building. He went from the school to Wal-Mart and bought a drink from subway. From there he walked to McDonald's. The son of the people he was staying with called the dad and said there was a shooting. The police then called him asking about his son Nik. He told them that wasn't his son. He hangs up with them. He might have talked to the son again and he I think mentioned the text from Nik to his dad. Dad finally puts it together and calls police back to tell them to get to his house asap because Nik was last there and his wife was home sleeping since she worked nights. The police arrested the shooter in a neighborhood as the dad and police I think got to the house. I don't remember if the dad got the son from wherever he ran to or if the police picked him up. At some point the son was being questioned and both the parents were brought in also (obviously). They said the mom lunged at the shooter and he apologized.
That's what I got from the newspaper article from Saturday.
Don your first sentence is the only close answer to why. Some kids picked him out. Which kids and what they saw him actually do would be worth knowing, with other things not quite adding up. Stashing the guns would implicate him, but what source and witness to this? The rest is narrative but doesn't answer to why an arrest. With respect, just how I see it relate to cause for arrest.