I totally understand what you're saying but I think that we're just going to have to agree to disagree on this one.
I'm not saying that LE has information that will cause Raven to hang himself. What I'm saying is that if LE has a bunch of circumstantial evidence with no hard evidence behind it, they can't be sure that it will be enough to convince a jury. So if they take it to court on the hopes that the CE will be enough to convict him, and fail, then Raven walks free. As you know, they cannot try him for the murder a second time - they will have lost the case for good.
So if LE has only CE, they may want to let him roam freely, monitoring him along the way, and hoping for him to slip up. Maybe waiting for a girlfriend to come out of the woodwork, maybe waiting for a life insurance claim to be filed, etc. It wouldn't be the first time that LE has had to sit back and wait for something more solid in order to try a case. Anyway, that's what I meant by "giving him enough rope" - basically just giving him enough room for him to forget himself. Yes, it has been three months. But that's really not that long if you think about it. If he did commit this murder, how much time would it take for him to begin to feel like he's gotten away with it? I don't know but I would suspect longer than 3 months. I think that once 6 months or 9 months or a year goes by, the perp gets more and more careless. Life goes on, and you forget that people might be watching you; might still be building a case against you. And if there's no hard evidence, unfortunately this investigation might have to move into that mode.
Finally, we don't know if the lab work has come back yet. From what we've heard about the back-up in NC, it seems quite possible that it hasn't. I can't imagine LE making an arrest without first having those results, no matter how strong their suspicions might be. Once they charge him, that clock might start ticking for a speedy trial. IMO, there's no way they want to risk starting that clock without having each and every single shred of evidence possible, especially if it comes down to being mostly circumstantial.