Another three persons not employed by TLT were likewise arrested.

The investigation focuses on procurements for the purchase of second-hand buses carried out since 2012. Of the four persons in managerial positions at TLT, one is accused of taking bribes during the period from 2012-2017 in return for specific companies receiving an advantage in the procurement of second-hand buses as well as procurements for repair and maintenance contracts and provision of goods, spokespeople for the Office of the Prosecutor General said.

The total amount of assets received as a bribe amounts to €2 million.

The detained managerial employees of the public transport company are TLT board member Alar Urm, Andres Herkel, director of the traffic service at the company, Hannes Erbsen, manager of repair workshops, and Jaanus Vink, deputy manager of repair workshops, spokespeople for the city government said.

Officers of the Central Criminal Police are currently conducting procedural acts on the premises of TLT's bus operations unit.

The three other individuals arrested who are not employees of TLT are connected with the provision of goods and services to the company.

Mati Ombler, head of the Office for the Investigation of Corruption Crimes at the Central Criminal Police, said that businesses and municipalities must pay particular attention to potential fraud when purchasing goods and services, and do everything possible to reduce the risk of corruption.

"To prevent wrongdoings, we advise managers to keep an additional eye on procurements and large-scale purchases, which should exclude the possibility of infeasible use of assets and someone earning unjust income," Ombler said.

Special Prosecutor Leelet Kivioja, the prosecutor heading investigation, said that the procedures conducted on Tuesday were the first public procedures in a criminal investigation launched last summer.

"By now we have gathered enough evidence to detain seven men as suspects in a criminal offense," Kivioja said. "For two of them, the Prosecutor's Office intends to seek custody from a court of law."

The investigation is supervised by the North District Prosecutor's Office and conducted by the Office for the Investigation of Corruption Crimes of the Central Criminal Police.

CEO: We are going to fire Vink, suspend others

TLT CEO Enno Tamm said that no one should be declared guilty before a verdict by a court of law, let alone before the details are known. He said that in-house audits conducted at TLT have revealed several inconsistencies which have raised questions. Unfortunately, he added, the internal audit does not have the right to carry our procedural acts.

Tamm explained that on the basis of the findings of an internal audit, the company's management board arrived at the conclusion on March 28 that Jaanus Vink must be fired from his position.

"We were overtaken by events, however," he continued. "Our next steps now will be to dismiss Vink from his office and suspend the others, pending the outcome of the probe."

He described the situation as very unpleasant and saddening, but added that the company would do its utmost to defend its trustworthiness and good name.