6:19 AM PT -- We've learned the father of the student who made the threat later met with police and turned over a black handgun, a magazine, 6 bullets and an airsoft pistol.

A student at Marjory Stoneman Douglas High School made threats with a gun and ammunition against another student, and parents want to know if more danger lurks on campus ... yet the school has gone radio silent.

A student at the school posted these ominous pics with a clear target ... a fellow student he accused of stealing his Gucci sandals. The student in question posted this ominous warning, "Catch me out here n****," along with, "Anyone know josh at Stoneman Douglas he's light skin where's Gucci glasses and jeans that look like a 4 year old drew on em hmu."

Cops came to the school last week and arrested the student for making criminal threats. He told cops the bullets were his dad's and the gun was real ... it was a BB gun. And there's this ... according to the police report, his Fortnite gamer tag name is NickCruz ... the same name as the notorious shooter.

The parent of the student who was targeted went to the school to find out if the student who was arrested would be back on campus. According to the parent's lawyer, Bradford Cohen, the school refuses to give an answer, which has freaked out a number of students and parents.

Cohen tells TMZ this is not about suing the school ... it's purely about safety.