There is no question there were issues with the investigation. Yes, that happens in just about every case, but shocking for a case this high profile. They literally had a video of the murderer, and no one recognized him or his clothing. I truly believed it would be solved within days or weeks, but that's obviously not what happened.
Years went by, press conferences were held, and new information was released to generate tips. Yet this case wasn't broken by those efforts. It was broken by something they already had; a glaring piece of evidence. They had a statement from a man who admitted to being there that day, around the same time that the girls were there.
The follow up interview was damning, as Allen admitted to wearing the very type of clothing that witnesses saw him wearing, and that video captured the killer wearing. That provided the probable cause necessary to execute the search warrant that ultimately linked his gun to the unspent round found between the girls' bodies.
We don't know what else that search warrant turned up, especially the results of any testing. But imagine how much more fruitful it would have been had they done it years before. It appears that he even kept the jacket in question, which would no doubt have been covered in blood after the murders. They very well could have had him dead to rights, where there would be no room for any debate as to his guilt or innocence.
So yes, this was a flawed investigation. At the same time though, it was a thorough one. They looked at RL very hard, executing search warrants on his property, and pushing as far as they could until they reached a dead end. They likewise honed in on several other potential suspects, to include Kegan Kline, who looked really good for it in many respects. Yet they didn't pull the trigger, because the evidence was not there.
I do not believe for a second that hair grasped in the hand of a murder victim was not tested. Even if they knew it was female, it's potentially a link that could immediately bring a killer from the darkness, into the light. I think once this is addressed by the prosecution, it will show that it was in fact connected to Libby's female relatives, and they stopped at that point.
Allen says he was there. Witnesses say he was there. His gun says he was there. He was dressed like BG. It's pretty hard to claim investigators had tunnel vision here.