George Whitmore Jr., an eighth-grade dropout whose confession in 1964 to three New York murders he did not commit had a decisive role in the Supreme Court’s Miranda ruling protecting criminal suspects and in the partial repeal of capital punishment in New York State, died on Oct. 8 in a nursing home in Wildwood, N.J. He was 68.

The cause was a heart attack, his daughter Regina Whitmore said.

Mr. Whitmore was 19 in April 1964, when he was picked up on a Brooklyn street for questioning about an attempted rape in the neighborhood the night before. A soft-spoken young man, he had grown up in a house in a junkyard that his father owned in Wildwood. After trying hard in school but dropping out at 17, he moved to Brooklyn and was waiting for a ride to work when the police car pulled over.

At first he was pleased that the police were asking for his help in solving a crime, he later told interviewers; he would have a good yarn to tell his friends, he thought. But when his interrogation ended several days later, Mr. Whitmore had confessed to the attempted rape, and more. He also confessed to the rape and murder a few weeks earlier of another woman in the neighborhood, Minnie Edmonds, as well as to the murder of two young women in Manhattan in August 1963. Their bodies had been found bound and stabbed numerous times in the apartment they shared on East 88th Street.

Called “the Career Girl Murders” in newspaper headlines, the killings of Janice Wylie, 21, a researcher at Newsweek magazine, and Emily Hoffert, 23, a schoolteacher, had been under investigation for eight months.