There is a subtle difference between the two accounts, in that the Vallejo Times-Herald newspaper article refers to peeling rubber, whereas the Debut of Zodiac letter alters this to squealling tires. When we take a look at page 15 of the Blue Rock Springs police report regarding George Bryant, it states that after the gunshots ceased "he then heard a car take off at super speed and it burned rubber and was squealing its tires as it sped along the road".
It can be seen that the "Zodiac Killer" in the August 4th 1969 Debut letter described squealling tires, while the police report on July 7th 1969 described the car as squealing its tires. Is this an unfortunate coincidence of common phraseology, or did the author of the Debut of Zodiac letter inadvertently use the language he had read in the Blue Rock Springs police report?.