This has nothing to do with the 1st or 4th Amendment.
He would have a 1st Amendment right to go on television and read a statement saying he shot that person with criminal intent, and that it was premeditated. He could also confess to any other number of crimes, under the 1st Amendment.
So he had the right to do it, but that doesn't meat it would help his legal issues. So, this has nothing to do with his rights.
He has a 1st and 4th amendment right to associate and to speak why such association is consistent with his defense. PBs are pro 2nd amendment and make no secret of it.