The five knife wounds to the front torso and right arm of Cheri Jo Bates were almost certainly delivered while the young woman was standing upright (likely restrained by the killer from behind). The initial part of the attack to this region was probably over in as little as five seconds. She was then likely thrust forward, face down, into the position her body was eventually found on the driveway floor. It is in this position the sixth knife wound was "plunged into her". When the Confession letter author mailed their two typed letters on November 29th 1966, this strike was described as the one prior to "cutting her throat". The sequence of the attack described in the letters matches with the findings in the autopsy report. But crucially, the author stated "I plunged the knife into her and it broke".
During the initial part of the attack Cheri suffered a "1.7 cm mainly transverse fresh laceration of the skin of the left chest over the 5th rib and centered about 2 cm medial to the left vertical nipple line". This produced a "1.5 cm oblique cut in the bony portion of the 5th rib anteriorly on the left corresponding somewhat to the skin lacerations over it". This is the only damage noted at autopsy to the hard skeletal structures of her body. It is at this point the lock mechanism of the knife was most likely compromised. The knife may still have appeared functioning, but it's possible that the blade was not fixed in position (see here).
If this bone injury was the fifth knife wound administered to the front of her body before she was thrust forward to the ground, a faulty lock mechanism, weakened during this strike, would have meant that the sixth and final stab wound glancing the transverse process of her spine "2 cm lateral to the midline and opposite the spinous process of the 7th thoracic vertebrae", would have alerted the stabber to the malfunctioning knife blade - which was described by the Confession letter author as a knife that "broke". However, a knife in this condition can still function perfectly well as a slicing tool. A right or left-handed person drawing the knife across their victim's neck would effectively keep the blade open. The author describing the cutting of her throat immediately after they "plunged the knife into her and it broke", is a possible consequence of the prior strike and the rib injury detailed at autopsy. It also shouldn't be forgotten that the Confession letter author mentioned "her breast felt very warm and firm under [his] hands". when we consider that all three wounds to her front torso were to her breasts.
Andrew Gray, an excellent Zodiac researcher, speculated why a hoaxer would need to add the phrase about the broken knife into the typed Confession letter, because this appears like an unnecessary addition to a letter if you are a hoaxer. This statement seems like an admission only relevant to somebody who was present in the moment. Somebody who needed to explain why the knife attack was brought to a premature end.
During the initial part of the attack Cheri suffered a "1.7 cm mainly transverse fresh laceration of the skin of the left chest over the 5th rib and centered about 2 cm medial to the left vertical nipple line". This produced a "1.5 cm oblique cut in the bony portion of the 5th rib anteriorly on the left corresponding somewhat to the skin lacerations over it". This is the only damage noted at autopsy to the hard skeletal structures of her body. It is at this point the lock mechanism of the knife was most likely compromised. The knife may still have appeared functioning, but it's possible that the blade was not fixed in position (see here).
If this bone injury was the fifth knife wound administered to the front of her body before she was thrust forward to the ground, a faulty lock mechanism, weakened during this strike, would have meant that the sixth and final stab wound glancing the transverse process of her spine "2 cm lateral to the midline and opposite the spinous process of the 7th thoracic vertebrae", would have alerted the stabber to the malfunctioning knife blade - which was described by the Confession letter author as a knife that "broke". However, a knife in this condition can still function perfectly well as a slicing tool. A right or left-handed person drawing the knife across their victim's neck would effectively keep the blade open. The author describing the cutting of her throat immediately after they "plunged the knife into her and it broke", is a possible consequence of the prior strike and the rib injury detailed at autopsy. It also shouldn't be forgotten that the Confession letter author mentioned "her breast felt very warm and firm under [his] hands". when we consider that all three wounds to her front torso were to her breasts.
Andrew Gray, an excellent Zodiac researcher, speculated why a hoaxer would need to add the phrase about the broken knife into the typed Confession letter, because this appears like an unnecessary addition to a letter if you are a hoaxer. This statement seems like an admission only relevant to somebody who was present in the moment. Somebody who needed to explain why the knife attack was brought to a premature end.
2 cm lateral to the midline and opposite the spinous process of the 7th thoracic vertebrae