Venezuelan journalist Jesús Medina was asking government officials Friday to return the equipment that they seized when he was detained this week.
A Venezuelan judge ordered Sunday that Medina and two foreign journalists, Roberto Di Matteo from Italy and Filippo Rossi from Switzerland, be released from prison.
The National Union of Press Workers reported National Guard agents arrested them while at the Tocorón prison in the central state of Aragua, one of the most dangerous prisons in the country.
They were detained Saturday while working on an investigation at a state prison in Aragua. Medina said they were not working undercover, but had made appointments with officials who were aware of their work.
Venezuela has some three dozen prisons that face serious problems of overcrowding and violence generated by gangs that internally control prisons and smuggle weapons and drugs.