It is possible he was murdered, but it just seems unlikely.
You'd have to get a guard to do it. And for a guard to do it, they'd have to get other guards in on it. Because you'd need to minimize witnesses - get Epstein's cell mate out of there, get him off suicide watch.
Plus, this was the second suicide "attempt." So if it were murder, that means they failed the first time, then came back again to do it, despite heightened security around the guy. I just can't imagine being a prison guard and thinking that was worth any amount of cash. Besides, then you'd have to hide that cash. Imagine being the guy on suicide watch for Epstein, Epstein dies, then a few weeks later you bought a Porsche and a vacation home.... The motive sucks.
Sure, people get murdered in prison, Usually by other inmates. When it happens by guards, there's usually a huge rift between a certain guard and a certain prison - just like on the outside - two people just have it out for each other. It's predictable.
Want to know a way cooler theory?
Someone with a lot of cash said they'd murder Epstein's family if he didn't hang himself. Think about it. You are a loaded world elite type person, and Epstein's about to spill the beans on you. You tell Epstein if he doesn't do it, even in a coded message or something, his family is gone. If he kills himself, their lives would be spared. Elites would definitely have the power to do that.
So Epstein tries to do it once, gets cold feet, or otherwise just fails, and says someone tried to "murder him," because he doesn't want to be put on suicide watch, making his plan impossible. So he waits for the opportune moment (no cell mate, no suicide watch guard), and bam, he does it.