Reina Luisa Tamayo, 62, accompanied by Cuban-American Sen. Marco Rubio, R-Fla., denounced Fidel and Raul Castro as "murderers" in an emotional visit to Capitol Hill Tuesday, McClatchy Newspapers reported.
Her son, Orlando Zapata Tamayo, died at age 42 in February 2010 after an 85-day hunger strike at the Kilo 7 prison in Cuba's Camaguey province.
"I would go to every corner of the world to ask for justice for the cause of my son who was assassinated," Tamayo said, holding a blood-stained white T-shirt her son gave her shortly before he died. She said the blood came from beatings by guards, who refused him water.
Zapata wrote on the garment: "My blood is in service to liberty for all 11 million Cubans."
Rubio took the occasion to criticize President Barack Obama for loosening curbs on U.S. travel to Cuba.
Tamayo arrived in Miami in June with her son's ashes, which were buried at the mausoleum for fighters in the 1961 Bay of Pigs invasion.