The STT informed that Račkauskas is suspected of influence peddling and abuse of official position, and the mayor's advisor and the three business representatives are also suspected of influence peddling.
Račkauskas' phone has been turned off since Tuesday mporning.
Sources told BNS Lithuania the STT questioned Panevėžys' deputy director of administration Tomas Jukna as a special witness.
The STT suspects that municipal administration employees were given unlawful instructions to create favorable conditions for some companies to win public procurement contracts. It is suspected that bribes were offered for favorable decisions in the form of services.
STT officials are looking into circumstances surrounding certain public procurement tenders in Panevezys, related to design and document preparation.
"Evidence collected during the pre-trial investigation provide reasonable grounds to suspect that promised favorably decisions were also paid in bribes in the form of services," the service says.
Sources told BNS Lithuania the investigation focuses on public tenders linked to the planned construction of a 50-meter pool as well as undergrounds containers and the municipal marketing program.
Račkauskas ran in the municipal election on the list of the Kartu (Together) movement. Almost all members of the municipal council, including the mayor, have left the movement amid disagreements with its leader MP Povilas Urbšys.