The Texas Chainsaw Massacre: The Case It's Based On
Some sources indicate that the original TCM was based on an unsolved series of murders known as the Texarkana Moonlight murders. Since Hooper has never said so, and since those murders bear little relation to the violence in TCM, this seems a bit far-fetched. However, this series did take place in Texas, which gives the movie, as an "actual incident" type of picture, more of an authentic feel.
A full moon was out on February 20, 1946 (some say the 23rd), when two teenagers were attacked in their car, and the girl was raped, but no one died during this incident. The attacker, a tall man wearing a white mask, used his gun to bludgeon the boy, Jimmy Hollis. Apparently an approaching car frightened the attacker away and the police were unable to identify a suspect.
Then a month later and a mile away, also under a full moon, another couple was similarly attacked. It was March 23 when Richard Griffen was in the car with his girlfriend, Polly Ann Moore, and both were shot in the head from behind with a .32. Investigators thought that they had been killed outside the car but then placed back into the seats. The motive for this behavior remained a mystery, as did the perpetrator. The next couple to endure such treatment was treated quite differently.
In April, fifteen-year-old Betty Jo Booker and her boyfriend, Paul Martin, were slaughtered, with evidence that Betty Jo had been raped and tortured for hours. The body of her boyfriend, Paul Martin, had been dumped more than a mile away. He, too, had been shot. Since the bullets had come from a .32 revolver, investigators believed that at least the two shootings were related, and possibly the initial lover's lane attack. Tire tread impressions from all three scenes supported this linkage and the press gave the fiend a name, "the Phantom." There was more to come, by some speculations, but this time the victims would be older, attacked in their home.
In May, more than ten miles from Texarkana, an middle-aged couple was shot in their farmhouse, but the wife, Katy Starks, managed to escape and raise an alarm. She survived, and nearby, police found the tire tread impressions again. They also had muddy footprints from inside the house to compare to a suspect, if they ever caught one. Yet if the Phantom had committed this shooting, he had used a different gun, and it seemed at the time more likely that it had been a burglar looking for goods. In the 1940s, police tended to group similar crimes in an area to a single repeat offender, though ultimately, this crime was attributed to the Phantom.
Then the killings stopped and the murderer was never identified, although some believed that a man who had killed himself and incinerated his car—with attention to the tires—had ended the spree himself. There were other suspects as well, but clearly there's no relationship between this brief spree and the incidents in TCM, aside from the hit-and-run nature of the Phantom, which is similar to the Hewitt clan members in some of the sequels, and the white mask. Why it's even suggested as an inspiration seems a real stretch.
In any event, TCM spawned several sequels and a remake.