The Prosecutor General's Office said in a statement that evidence suggests Masiulis accepted a €106,000 bribe from Raimondas Kurlianskis, vice-president of the business group MG Baltic, in exchange for "decisions favourable and beneficial" to the company.
Prosecutors also say they have evidence that Masiulis could have promised to act in MG Baltic's favour himself and induce other individuals to do the same.
Masiulis, who showed up at the Prosecutor General's Office on Tuesday accompanied by his attorney Mindaugas Bliuvas, told reporters he came for questioning of his own will. He had previously pledged to cooperate with investigators and willingly gave up his seat in parliament which shielded him from criminal prosecution.
He rejected suspicions against him.
"Suspicions have been brought against me today and I can say at once that I dispute them," Masiulis told reporters, adding he regretted his involvement in the case which was "a hit to the entire political system" of Lithuania and caused "a crisis of confidence" in it.
Last week, investigators searched Masiulis' home and allegedly found a large sum of cash in marked bills. DELFI reports, relying on an unidentified source, that officers found €250,000 in Masiulis' possession.
Prosecutor Justas Laucius of the Organized Crime and Corruption Department has said that €106,000 came from Kurlianskis, while the provenance of the the rest of the alleged sum is unknown.
Kurlianskis, who is board chairman of a media company running several Lithuanian TV channels, has been detained on suspicions of influence peddling, bribery and unlawful possession of state secrets.
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