On page 194 of Innocents Betrayed Sandra Lean wrote, “A pouch, taken from Luke’s home, was said to belong to the ‘missing’ knife. But it is worth noting that the size of the blade used to inflict the wounds found on Jodi would have to have been considerably larger than the knife which fitted to the pouch. Indeed, when the professor was asked about the wound inflicted on Jodi’s tonsil (by the blade being plunged into her mouth), he demonstrated what should have been the ridiculous suggestion that the knife produced in court could have been the one which inflicted this injury—the professor showed the court that only by holding the knife at the very edge of the handle, with the tips of his fingers, could that knife have inflicted the injury without causing, for example, damage to the teeth and corresponding damage to the hand of the attacker (which was not found on Luke’s hands)." From what I gathered in a Scottish Sun article, I surmise that the blade was four inches in length.
From EdinburghLive, "'There were about ten officers, some in forensic suits, emptying the skip to try to find the broken tip. I read the brand name on the knife and checked online. I found an exact match, and it was very expensive.' At the time, a field next to Tom’s garage was used by teenage mechanic apprentices for racing stock cars. One of them, now a dad in his mid-30s, said: 'We found a knife with blood on it in the skip. We were like, ‘What the *******.’ It was terrible.'"
Of course the knife from the skip might not have been the murder weapon, but one only hopes that it was tested correctly.
