PRESIDENT RAÚL Castro of Cuba delivered a speech to the National Assembly last month in which he lamented the demise of Cuban culture and civility. He railed against bad behavior, from building houses without permits to shouting and swearing in the streets, from dodging bus fares to painting grafitti. “Living in society entails, in the first place, accepting rules that preserve respect for decency and the rights of others,” he declared.

The rights of others? Civility? Seven days after Mr. Castro spoke these words, the civil society group Ladies in White went on a march for freedom and human rights in Matanzas province. They’ve done this before, on other Sundays, in other towns. A group of Cuban government supporters forcefully cut off the march and proceeded to beat and harass the members of the group, which was founded by the wives, mothers, sisters and daughters of 75 political prisoners who were jailed in a crackdown a decade ago. The attack was just the latest harassement and intimidation of Cuban dissidents.

The kind of civility that is recognized all over the world as basic dignity — the freedom to speak and associate, to choose one’s leaders, to live without fearing a regime’s security services — is not on Mr. Castro’s mind. His regime continues to threaten and persecute those who dare challenge its legitimacy.

One of the most passionate dissidents in Cuba until his death last year was Oswaldo Payá, champion of a campaign to advance democracy with a national referendum. On July 22, 2012, he died in a car wreck along with Harold Cepero, the leader of the youth wing of Mr. Payá’s Christian Liberation Movement. The driver of the car in which they were riding was Ángel Carromero, a young Spanish politician who was visiting Cuba. Mr. Carromero told us in March that the car was rammed from behind by a vehicle which carried government license plates, after which he lost control of the vehicle.

Mr. Carromero has now raised fresh questions about the car wreck in an interview with the Spanish newspaper El Mundo, suggesting that Mr. Payáand Mr. Cepero may have been alive when they were brought to a local hospital and only died later, perhaps at the hands of a state that did not wish them well. He has no hard evidence, but suspicions linger. The family of Mr. Payáwas never given an autopsy report.

The most significant unanswered questions are: Who rammed the car on a wide and flat road that day? And why? Mr. Carromero’s latest comments reinforce the need for a thorough investigation. We were heartened to see that the new U.S. ambassador to the United Nations, Samantha Power, last week raised with the Cuban foreign minister the need for a credible investigation into Mr. Payá’s death. A similar demand came from the chairman of the Senate Foreign Relations Committee, Robert Menendez (D-N.J.). Perhaps it is too much to suggest that Mr. Castro might allow a genuine investigation into these tragic deaths, no matter where it leads. That would be truly civil.