Well the whole thing is kinda murkey. Since Clint says Garage and is clear about Garage, and the fact that he saw only silhouettes and it seems to have been dark I would say they were in the Garage. I assume there is a door at the back of the Garage leading to the Carport. Perhaps they were in that area?
Remember also Clint said he heard voices outside first. Then he saw the two people in the Garage. So, I assume at first they were outside and then moved into the Garage. Perhaps Holly was accosted by her car first and then the suspect led her into the garage area. Perhaps the dog barking and Clint looking in spooked him. During Clints interviews no one has pressed him for any kind of clarification or details.
It is murkey! Ok. Let's say it was someone that Holly knew. An ex for example. The ex, being close to the family, knew Clint was not suppose to be there so Holly would be alone. So he confronted her in the carport and was taking her back into the house to assault her. The dog would know him so at first wouldn't bark until it sensed Holly was in danger. Trying to figure out how Clint's version could have worked. Still if she screamed and Clint never heard it, doesn't make sense since the neighbor's son, dog's cousin, father-in-law's girlfriend half-removed did! :woohoo: