The Glasses and the Phone Calls
Here's my take but I'd like your opinion.
1-Matty held the glasses the whole time, and the story about the maid having them was false. Also, it was Mattie who contacted the D.A.'s office with the offer of the glasses. This was mostly to set Ned up at the boat house, but perhaps also to frame him legally (well, he was guilty) and clear her.
2-Matty or perhaps her friend (Mary Ann) intentionally called Ned's hotel room the night of the killing in order to erase his alibi about being in Miami.
What do you think?