There is a possibility the Zodiac Killer wasn't wiping down either the front passenger door handle or the driver's side door, as the front passenger door handle was not visible from their position across the street and the driver's side door handle area may have been obscured by the Zodiac himself and the three teenagers just interpreted his actions, based upon him holding what was considered to be a white rag or handkerchief, but could equally have been the Zodiac carrying the section of Paul Stine's shirt. But to exit the front passenger side door after securing a strip of Paul Stine's he should have simply just left the scene up Cherry Street. The fact he traveled around the taxicab to the driver's door, without opening it, does not leave many options as to why he performed this action, other than wiping away fingerprints and suggests the interpretation of events by the three teenagers was in fact correct.
There is a logical course of events that may explain a murder at Washington and Cherry Street, explain the blood pattern on Paul Stine's shirt and crucially the blooded fingerprints on the post to the rear of the driver's side door.
As Paul Stine parked up at the Washington and Cherry Street intersection the Zodiac placed the gun close to Paul Stine's head and fired. Back spatter from the wound struck Zodiac's hand and gun depositing blood onto both. He repositions his hand to put the gun away. Now at this point he could just leave the scene, but his objective was to secure a trophy, so he now had to access the front of the taxicab. In view of the blooded prints on the left post of the taxicab, this may suggest his possible
A big thanks to Randall Scott Clemons for his work on this topic.