I seam to recall reading somewhere that the step father was a cop for West Memphis although this article does not mention that fact. Have you read much on this case and if so am I mistaken?
One step Father was a police informer. He is the one who was portrayed as suspicious in the documentary. But the DNA which was found belongs to a different step Father.
Overall, there is a complete lack of physical evidence to convict anyone (IMHO) and it is probably too late now to believe that this case will ever really be solved.
Damien Echols, however, is more than just a little weird. He also seemed to enjoy the attention--until he got to prison and became someone's b*tch. He's complained many times about prison rape.