Caylee's one hair was found in the trunk of the car with root banding consistant to decomposition and it wasn't enough to convict. I seriously doubt one single hair belonging to TH would have convicted him of 3 counts of first degree murder.
We have a detailed confession and:
Fibers found on the victims’ clothes matched clothes seized from Echols’ and Baldwin’s homes. The prosecution presented this fiber evidence at both trials. Supporters argue that those fibers came from common material found in many homes and that the fiber matches don’t really connect Echols and Baldwin to the crime scene. Frankly, I side with supporters on this one. The fiber evidence was weak.
* Blue candle wax on one victim’s shirt was similar to blue candle wax found in Damien Echols’ bedroom.
* Police took a necklace from Echols when he was arrested. An outside crime lab later found blood from two distinct DNA sources on the necklace. One source was consistent with Echols himself. The second source was consistent with both victim Steven Branch and co-defendant Jason Baldwin.
So it’s not true that there was “no physical evidence tying the defendants to the crime”. The physical evidence just wasn’t overwhelming. Just as importantly, there was no physical evidence tying any other suspects to the crime.
http://wm3truth.com/the-west-memphis-three-were-guilty/physical-evidence-and-lack-thereof/