I don't think that it was an accident. At this point in time, I believe that Ross was at the very least negligent with respect to caring for Cooper. I am not sold on the premeditated part, and the prosecution will have a difficult time proving that.
To be honest, I am very skeptical about the "facts" surrounding this case. Detective Stoddard was very loose with his words. For example, he stated, "Ross returned to his car at lunch with his newly purchased light bulbs and placed his head inside the car." However, the surveillance video clearly shows that Ross did not put his head inside the car. He either had one or two arms in the car and tossed the light bulbs on the front seat. He likely did not even have a line of sight to Cooper's car seat. There are an insignificant number of instances like this. I am eagerly awaiting to see the evidence presented at trial.
While i do not currently think that this was premeditated, I do believe that Ross was negligent.