There is an extremely interesting article on the Howard Davis website 'The Zodiac/Manson Connection' regarding the autopsy findings of Paul Stine. Here is a small excerpt;
"The last issue I wish to discuss was a finding in the coroner's report that I cannot yet resolve. Mr. Stine's lungs were described as follows: "Both lungs are moderately increased in weight. There is congestion at the base and dependant portions. Multiple intraparenchymal hemorrhages are noted." The blood in the lungs does not appear to have drained from the head wound. Were this the case the blood should be in the lung air space rather than the parenchyma (which is the lung tissue itself.) Additionally, the position of Stine's body (with the head approximately at the level of the chest while in Zodiac's lap and then below the level of the chest, on the floorboard after Zodiac left the scene) would not be conducive to passive blood flow from the head wound into the air space of he lungs." http://www.zodiackillerthemansonconnection.com/autopsy_interpretations.html
Intraparenchymal injuries are noted frequently in automobile crashes, where traumatic brain and chest injury occur as a result of the vehicle being brought to a sudden and immediate stop. "Lung parenchymal injury: Pulmonary contusion is caused by rapid deceleration against a steering wheel, fall from a height and from blast injuries." See here.
The phenomenon of chest injury, such as parenchyma damage, without rib breakage or fractures is widely covered with a cursory internet search. If this anomaly in Paul Stine's lungs is not as a result of natural causes, which as Howard Davis states "is unlikely," then we have to consider injury caused by an external force.
Has the narrative of the Paul Stine murder become so firmly entrenched, that it is inevitable the proposal of an alternative hypothesis will be widely disregarded. Was it really as straight forward as 'Paul Stine pulls up at Washington and Cherry and is shot', or is there another possibility incorporating these autopsy findings.
If the taxicab had experienced rapid deceleration, then it would not be uncommon to sustain chest injuries from impacting the steering wheel or from a seat belt injury, and the rear passenger would be catapulted forward, striking their hips or lower legs against the back of the front seats, explaining the observations of Donald Fouke.
There had been a spate of taxicab robberies in the run up to the Paul Stine shooting and the murder of taxicab drivers was not uncommon. The wanted poster issued on October 13th 1969 was testimony to this fact and no doubt Paul Stine was fully aware of the risks his profession entailed.
If the taxicab was still in motion when the gun was presented, the actions of Paul Stine would be instinctual, he can comply or react. If he slammed on his brakes fully, he may feel he can disable the assailant, as the passenger would be unprepared for the rapid deceleration, albeit he would still strike the steering wheel. Had this occurred, clearly it ultimately failed, as the assailant regained control. In the absence of any skid marks just prior to the intersection of Washington and Cherry, it may indicate that this occurred at Washington and Maple, or even earlier in the journey. Whether we believe the routinely told story of Presidio Heights on October 11th 1969, that the murder occurred adjacent to 3898 Washington Street, it still cannot rule out what could have proceeded it. Had Paul Stine valiantly attempted to disarm the assailant precedent to his murder, an attempt that would ultimately fail, but indelibly left its mark at autopsy and left the Zodiac Killer shuffling down Jackson Street.