5:30 AM PT -- Police have arrested Dedrick D. Williams for the murder of XXXTentacion. Broward County Sheriff's Dept. took Williams into custody Wednesday evening.

Investigators working on XXXTentacion's murder seem to be homing in on a Florida rapper who posted a pic of himself packing heat Monday, not far from the crime scene.

Soldier Kidd's been widely accused online of having possible involvement in XXX's shooting death -- mostly due to a photo of himself at Hook Fish & Chicken restaurant, which is 7 minutes from where X was killed.

In the pic, you clearly see a handgun in Kidd's lap, right next to his food. It was posted within an hour of X's shooting.

We're told detectives went to Hook Fish & Chicken late Monday to collect surveillance footage -- specifically of the time Soldier Kidd was there.

There's more -- according to the dispatch audio from the shooting, one of the 2 armed men was wearing a red mask. Kidd shared a photo of himself and a friend with a red mask in the front seat of his car.

The "Triple X" isn't necessarily a reference to XXXTentacion ... since Kidd recorded a mixtape with that title.

We're told cops have also collected security footage from the motorcycle shop where the shooting went down. Police haven't named any suspects, and Soldier Kidd has denied any involvement.