Touch (or transfer) DNA is always partial. It’s not necessarily indicative of somebody (ie the killer) actually touching the girls. DNA particles (from shed skin, hair etc) are everywhere and can attach themselves to clothing just by sitting where someone else has sat, being in somebody’s vehicle, wearing somebody else’s clothing who was near someone etc. Touch DNA would not convict anyone without other additional evidence to identify any one suspect actually committed the murders.
LE have said they don’t know if they have the killers DNA. They’ve also stated DNA can be found at every crime scene.
An outdoor crime scene accessible by anyone who walked there, bodies not found until the following day, would be different in expectations than say, finding than a killer’s DNA in a house on such things as doorknobs, on the floor or on other hard objects especially if the accused had no justifiable reason for being in that home.
DNA isn’t required to successfully prosecute when other incriminating evidence is present. I’ve gotten the strong feeling all along, this case isn’t going to solved by DNA alone and that’s why LE have consistently asked for that one important tip from somebody who knows who the killer is.
JMO