The disappearance of Petko Sertov, a former head of the State Agency for National Security (DANS) is not an abduction but was carefully planned, a lawmaker familiar with security structures has said.

Sertov, who has been missing for a fourth consecutive day, "carefully planned" his actions, leaving both his mobile phones home to depart in his car on Friday afternoon, Mincho Spasov, a former head of the Internal Affairs Committee, believes.

"The truth is that Sertov had interactions with Aleksei Petrov, but no speculations around him have been confirmed," Spasov told the Bulgarian National Television, referring to former agent Aleksei Petrov, a businessman and former secret agent often accused of being connected to the criminal underworld.

Media reports suggest police consider Sertov either dead or abducted, while people who know him outline a total of three hypotheses. The first involves suicide (as he owns a gun legally), the second (according to a former colleague) involves a trip for a hotel booking of which his wife was not informed.

In the third one, he is being pressured into disclosing information to which he had had access as head of DANS and of the later of an anti-corruption unit and which was harmful to certain political economic interests.

Some outlets raise the hypothesis that his disappearance was related to the latest developments around South Stream.

Sertov, 58, was the first head of DANS after the agency was set up in 2008 out of previous structures.

He later took the Deputy Chairman's position at the controversially perceived Center for Prevention of Organized Crime and Corruption (BORKOR), the anti-corruption unit with Bulgaria's Council of Ministers, but was dismissed in 2011.

He is currently retired, though he occasionally takes part in international security projects as an expert.