Don't need to leave DNA at a crime scene to be guilty. There are other ways to link one to a crime scene
Before the advent of DNA processing, people were caught and convicted of crimes all the time. DNA certainly isn't the only smoking gun. It also never reveals intent. You could prove someone was at a location, but can't prove what they did or didn't do.
I personally believe that he was involved, but I couldn't convict him based upon my uneducated beliefs.
Of course, DNA now often clears people of crimes they didn't commit.
I'm no bleeding heart liberal, but I hate the idea of a person rotting in prison for a crime they didn't commit.