ON MOST days, José Daniel Ferrer is hard to miss in Cuba. He’s often voicing criticism of the government on Facebook and Twitter, urging people to lose their fear of the authorities and speak up for their rights. Mr. Ferrer is leader of Cuba’s most active opposition group, the Patriotic Union of Cuba, or UNPACU, based in Santiago de Cuba. He has been through a lot, including years in prison, and yet never ceased being an advocate for democracy.

Until now. Mr. Ferrer’s voice has not been heard since Oct. 1, when he and others in his group were arrested without charge. Two were released, but Mr. Ferrer and several others have all but disappeared. Although in recent years the Cuban political police have periodically detained Mr. Ferrer for a few days at a time, this stretch is longer and Mr. Ferrer has been held incommunicado. His family is demanding that the authorities provide proof that he is alive, explain the grounds for his arrest and permit visits. Some activists in his group have told independent Cuban journalists at the news site 14ymedio.com that he is being framed on a criminal charge of carrying out an assault that didn’t happen.

It should be no mystery why he was arrested: to silence him. UNPACU has proved to be resilient and Mr. Ferrer quite steadfast in speaking out against the Cuban police state. He was among the 75 activists imprisoned in the “Black Spring” of 2003. He and about 50 others were supporters of the Varela Project, a citizen initiative for democracy championed by Oswaldo Payá, who was later killed in a suspicious car wreck.

Cuba’s rulers have tried mightily to suppress voices such as Mr. Ferrer but can’t silence them entirely. Although the regime inspires fear, dissent still bubbles up, and Cubans have lately been eager to take advantage of slightly improved mobile Internet connectivity to share complaints about everyday hardships, including fuel shortages and power blackouts caused by the drop-off of oil imports from Venezuela.

On Oct. 7, a group of 19 independent Cuban news outlets, many of them digital news sites, published a rare and revealing open declaration protesting attacks on journalists working in the country, saying in recent months there had been “a noticeable increase” in assaults and pressure on the unofficial and non-state press, including arbitrary arrests, interrogations, psychological intimidation, house searches, prohibitions on leaving the country, sexual harassment and defamation, among other things, all “part of a systematic campaign by the Cuban government to silence independent journalists.” The journalists demanded the repeal of laws that restrict freedom of expression and insisted that independent journalism be legalized. The declaration was a gutsy and laudable moment of speaking out without fear, just the approach Mr. Ferrer had urged.

Now he must be freed. Cuba’s communists ought to realize by now that they cannot jail free speech, no matter how hard and often they try.

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