Why wasn't connor's death 1st degree? He certainly knew he was killing him too...So very, very sad.
My guess is that it has to do with what this jury thought the motive was. They must have thought (wrongly, IMHO) that he wanted LACI out of the way for his other life. Or for his freedom.
Unfortunately, I feel that it was Connor who was the ultimate victim. He was able to fool around on Laci all he wanted. Connor was what was going to saddle him for life. Remember, he also NEEDED to be thought of as the great guy. If he divorced Laci, her family would have hated him. If he didn't pay up for Connor, he would have looked bad. Connor was the ultimate threat to his freedom (and sociopathic "fun").