S1 Ep3: Unplugged

After several months of wedded bliss, Fred discovers his wife, Ethel, has a well-kept secret. The next weekend, Ethel takes their deep-sea fishing vessel out alone, as she often does, but never returns. Her drowned body is later picked up by the Coast Guard, along with the boat, which sank. A week later, a new piece of evidence is reeled in. Just the evidence needed to arrest Fred for her murder. What was the evidence? How did Fred kill ethel?