Allen's shoe size (10.5) and glove size were the same as the killer's. He owned and regularly wore a Zodiac-brand sports watch with the same logo as the killer. Allen lived in Vallejo, across the street from where one of the first victims (Darlene Ferrin) worked, and near where one of the killings took place. When interviewed by police, Allen mentioned without being questioned that he had bloody knives in his car on the day of the Lake Berryessa attack, claiming they were covered in chicken blood. Allen also stated that he was a fan of the book The Most Dangerous Game, which the Zodiac killer had alluded to several times in his letters.
Perhaps the most significant evidence against Allen were statements made by a former acquaintance, Don Cheney. Cheney told the San Francisco Police Department that Allen told him that he wanted to kill people (including children) and told him exactly how he would go about doing it. He also mentioned the name Zodiac. Allegedly, these statements had been made before the actual murders took place.
While many believe that Allen was the Zodiac killer, Allen had been cleared several times during the investigation of the murders and the simultaneous hunt for the killer. These included passing a polygraph test, clearing a fingerprint screening (from those left at the crime scene of the taxicab murder), clearing a handwriting test and, most recently in 2002, being ruled out by a DNA test conducted based on DNA collected from one of the stamps of the Zodiac letters.
Book and film
Robert Graysmith's book identifies Allen as the Zodiac killer. The 2007 film Zodiac by David Fincher thoroughly makes a case for Allen as the killer. A notable theory that was presented in the film and the book is that Allen knew and dated Darlene Ferrin, one of the first victims of the Zodiac killer. The film also suggested that Allen did not work alone, and that his letters or other parts involved with the murders were not all done by him. This would explain why the evidence never fully matched for Allen.
