Alan Gross, imprisoned for five years in Cuba for his efforts to assist its Jewish community, said of Cuban leader Fidel Castro: “history will never absolve him.”

Castro’s death at the age of 90 was announced on Friday night by his brother, Raul Castro, Cuba’s current president.

“History will never absolve him. But perhaps now the voices of Cuba will be heard. Speak up, Cuba,” Gross tweeted shortly after Fidel Castro’s death was announced.

In later tweets he called for the United States to lift its embargo on Cuba.

When he was arrested in 2009, Gross, of Potomac, Maryland, was working as a subcontractor for the U.S. Agency for International Development setting up Internet access for Cuban Jews.

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Cuba’s deceased leader Fidel Castro

Gross was released in December of 2014 as part of a broader exchange in which three Cubans convicted for spying were released from American prisons. The same day, President Barack Obama announced renewed ties with the communist nation.

Gross has called for improved ties between the United States and Cuba. In September, he endorsed then-Democratic presidential candidate Hillary Clinton, citing in part her commitment to the Obama administration’s new openness to Cuba.