While Brett may be the most likely suspect i'm wary because its usually someone you least expect, for example no one really new the killer would be Detective Miller's husband in Broadchurch until the final episode. 

Most the evidence points to him but i'm guessing there's going to be a big twist and its someone we least expect.

It's clearly not Patrick, how could he save himself in the series 2 finale ?

Roll on Season 6 !!