Mr. Polanski was in London while his wife and several friends were staying in the main house at an estate rented by Mr. Polanski. The houseguests who were killed were Abigail Folger, 25, heiress to a coffee fortune; Jay Sebring, 35, a prominent hairstylist; and Voytek Frykowski, 32, a friend of Mr. Polanski’s. The other victim was Steven Parent, 18, who had stopped by to visit a friend, a caretaker at the estate, and was killed outside.

Dipping into the blood they spilled, the killers scrawled “Pig” on a door at the scene of the Tate killings. The next night, at the home of Mr. LaBianca, 44, who owned a grocery store chain, and Ms. LaBianca, 38, the killers used the victims’ blood to print “Death to Pigs,” “Rise” and “Healter Skelter” on walls and a refrigerator door.

It became known later that one scrawl was meant to be “Helter Skelter,” after the Beatles song. For Mr. Manson, the term had come to symbolize an Armageddon-like war between whites and blacks. He had convinced some of his followers that the killings would help foment this war, somehow enabling his “family” to survive and prosper. Mr. Bugliosi later titled his book about the case “Helter Skelter.”

Strangely, despite the similarities in the Tate and LaBianca killings, the police did not initially link them. After small amounts of cocaine and marijuana were found in the house where Ms. Tate and her friends had been staying, detectives speculated early on that those murders had been drug-related and not tied to the LaBianca killings. No drugs were found at the LaBianca home. And the LaBiancas, though well-to-do, were not celebrities like the first victims.

Image Mr. Bugliosi in 2008. Credit... Toby Talbot/Associated Press

Mr. Bugliosi wrote that the investigation had been hampered not only by premature assumptions but also by miscommunication within the Los Angeles Police Department and between the police and the Los Angeles County sheriff’s office. At the time, the sheriff’s office was investigating the killing of a man just days before the Tate-LaBianca murders. In that crime, also committed by the Manson family, the victim’s blood was used to write “Political Piggy” on a wall. Yet the various teams of investigators were slow to compare notes.