3 of the 4 suspects in XXXTentacion's murder knew each other and enjoyed flaunting their money together before the rapper was killed ... because there's video proof.
Dedrick Williams, Robert Allen and Trayvon Newsome -- who've all been indicted by a grand jury for first degree murder -- were in an Instagram vid posted by Williams weeks before X was shot to death in S. Florida ... trying to look poppin' while sifting through stacks of big bills.
The fourth murder suspect and alleged gunman, Michael Boatwright, is not seen in the vid.
As we've reported ... Williams and Boatwright have been arrested, but Newsome and Allen are still wanted. Police believe Newsome is a second trigger man.
It's been more than a month since XXXTentacion was gunned down outside of a motorcycle shop in Pompano Beach.