Previous articles state that the men were arrested on Feb. 5 and denied bail at their hearing a few days later. Smith was killed just prior to that. So as far as I tell, these guys were all in jail when Smith was murdered.
I wouldn't be so quick to discount Smith's murder serving as a message to the other team members. The article only says that this suspect is expected to testify against his "co-defendants." My bet is that he won't give up the larger operation and its orchestrator. (Yep, it was just us 5. Ya got us all.)
Further, prosecutors can "expect" all they want. Ken Starr wasn't the first or the last to be snowed into exchanging immunity for crapola. Less cynically--there is the possibility that word of this "expected" testimony is disimformation. Perhaps a trap using the suspect as bait? (Lessons learned from Katherine Smith?)