SOFIA (Reuters) - The man in charge of Bulgaria's communist secret police files has been found dead at his desk in an apparent suicide, but the two-day delay in announcing his death drew charges on Friday of a secret service cover-up.

Bozhidar Doychev, head of the National Intelligence Service archives, was found dead on Wednesday, having apparently killed himself for what prosecutors said were probably personal rather than work-related reasons.

Opposition legislators demanded an explanation for the delay in announcing Doychev's death and accused the secret service of a cover-up, noting that new legislation is in the works aimed at throwing light on murky corners of Bulgaria's communist past.

Bulgaria's now defunct Darzhavna Sigurnost was one of the Cold War's most notorious spy networks, and the files may contain the answers to some of the era's unsolved mysteries.

The network was implicated in plots ranging from the assassination attempt on Pope John Paul II to the "poison umbrella" murder of Georgi Markov on London's Waterloo Bridge.

"We were shocked by the fact that the death of such a senior intelligence officer was kept secret by the authorities," said Vesselin Metodiev of the rightist Democrats for a Strong Bulgaria. "There is a very unpleasant coincidence between this incident and a new law on the files."

The DSB called on President Georgi Parvanov to remove the head of the secret service and said the parliamentary commission overseeing the secret services should take over the archive.

The files are a highly sensitive issue in the Balkan state, which was the Kremlin's most obedient subject during the East-West confrontation of the Cold War era.

SLOW TO THROW LIGHT

Since the collapse of communism, Bulgaria has been the slowest of Moscow's former allies to throw light on the deeds of its secret agents and informants.

Rights groups and analysts say the failure to open the files has allowed ex-spies to use blackmail and other unsavory skills to take high-level posts in politics and business.

A parliamentary commission has approved a draft law to create a body to manage the files and check whether politicians, judges, public figures and journalists were spies, before Bulgaria joins the European Union on January 1.

But the main group lobbying to open the files says it faces stiff opposition from the secret service and the ruling Socialists -- reform successors to the former ruling Communist party.

"There are continuous attempts by the secret services and some deputies of the Socialist party to block the transfer of the files to the special commission," said Alexander Kashamov, a lawyer with the foundation Access to Information.

President Georgi Parvanov, a former head of the Socialists, and his successor Prime Minister Sergei Stanishev said earlier this year it was too late to open the files, though Stanishev later said he would clear up the problem.

Other leading Socialists played down the significance of Doychev's death. "I don't think this case is of great interest to the public," said Socialist Interior Minister Rumen Petkov.

(Additional reporting by Kremena Miteva and Tsvetelia Ilieva)