Definitely possible. Incarcerated celebs also face a unique threat in being surrounded by dead-enders with no purpose in life who may find meaning in just being remembered as, "the guy that nailed R. Kelly."
Yep. Having worked as an officer in NY State’s prison system for 25 years, I saw plenty. They wear their crimes as a badge of honor, and brag about it. I retired 16 years ago, and I’m sure it’s gotten even worse since then. And convicts hold grudges. They could have had a run-in with someone on the street, and years later, if they ran across that person, a friend, or a member of that person’s family, the grudge would be repaid.