Why do you think that Tui ran away and hid? From what I have read, it's believed that Matt was not the father of Tui's baby. That was likely a story that Al made up to throw the suspicion off of himself and the other clients who abused these girls. He likely fooled with the DNA samples to show that Matt was the father. Also, Matt couldn't get it up without a pill, as he admitted to his lady friend. Unlikely that he would have taken a drug to get it up for his daugther. And Tui had no memory of getting pregnant, so it must have happened when she was at Al's and after being given ruffies.
Tui wanted to go stay with Matt after she left the police station. She didn't fear him, so why did she run away. She couldn't have been afraid of Al at that time, because she didn't know he did anything. Recall how she was happy to go for the visit to his house at the end with her girlfriends. So who was she running from? Why hide? I couldn't figure that out. Also, wouldn't it have been likely that Jamie, her friend who was killed, would have told her what was happening? They were so close, she's pregnant and he never discusses it with her. Somehow he knew about Al and his games. Recall he referred to Al as the evil one or something like that.
I suspected Al almost from the beginning. When he was protecting Matt, I knew he was VERY corrupt. I was also shocked that Robin allowed Tui to go off with Al after the way he abused Jamie at the police station. She saw it too. Every fiber in her being would have said creep. Plus, there was her experience of passing out at his house that night. To be so smart, I found it difficult to believe that she didn't suspect Al more until the end.
Why do you think that Matt took off with the baby in the forest? Why did he take the baby and leave Tui? Where was he going? I suppose that one theory could be that he was indeed the father of the baby and he was going to get rid of the baby so the evidence of the paternity would not be disclosed. I don't know. It's not very clear.