Aaron Carter's trying to buy a gun and has threatened to harm family members ... at least according to anonymous callers who got cops to visit Aaron's house 3 times in a 24-hour span.
According to docs obtained by TMZ ... someone called St. Petersburg PD in Florida at 11:47 AM Tuesday saying Aaron has been trying to buy a gun in the last couple weeks. Cops went to his house, but no one answered the door.
They returned at 2:12 PM after another caller said Aaron needed psychiatric evaluation because he refused medical attention after a car accident. Police discovered Aaron had indeed totaled his BMW, and broke his nose, but was otherwise fine.
The third incident came at 4:18 AM Wednesday, when the caller said Aaron was threatening to harm family and others. Cops showed up, knocked on the door but someone shut off a light and closed the blinds.
We've reached out to Aaron's camp, so far no word back.