RIO DE JANEIRO, June 4 (Reuters) - Brazilian police arrested on Wednesday one of two suspected leaders of a paramilitary group believed to have tortured journalists with beatings and electric shocks in a Rio de Janeiro slum.

The journalists made the allegation on Sunday in their O Dia newspaper, saying they, along with their driver and a local resident, were captured and tortured by the group on May 14 while reporting undercover in the slum in the west of the city.

"We got to these people through the testimony of the victims," police commander Claudio Ferraz told reporters.

The two suspects were identified as Davi Leberato de Araujo, 32, and Odinei Fernando da Silva, 35, who police said were the leaders of the paramilitary group in the slum.

De Araujo, a prisoner serving time in a semi-open jail, was arrested. Da Silva, a police officer, is still at large, Ferraz said.

Paramilitary groups, often referred to as "militias" locally, are normally made up of off-duty or former police officers. They have spread in the city's violence-plagued slums in recent years, offering "protection" to residents from drug gangs.

They are now believed to control more than 10 percent of the city's more than 600 slums, often replacing the gangs' criminal networks with their own.

According to O Dia, its reporter, photographer and the two other victims were held by the armed men for more than seven hours during which they were given electric shocks, suffocated with plastic bags and forced to play "Russian Roulette" with guns.

The Paris-based Reporters Without Borders group sent a letter this week to Brazil's President Luiz Inacio Lula da Silva, his justice minister and the Rio state governor calling for a federal inquiry into the incident.

"Reporters Without Borders is stunned to learn this could have been carried out by members of the security forces who are supposed to combat crime and drug trafficking in sensitive neighborhoods," the letter said.

Human rights groups have long criticized Rio's police for brutal and corrupt practices in the war against drug gangs.

High-level security officials have been suspected of having close links with organized crime. (Reporting by Rodrigo Viga Gaier; Writing by Stuart Grudgings; Editing by Eric Walsh)

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