Respected news agency Reuters reported that eight cases of suspected insider trading were being investigated. In February Volkswagen offered $9.2 billion to acquire all shares in the Swedish company, but the deal has yet to be accepted by the Scania board.
A spokeswoman for the Economic Crime Authority (Ekobrottsmyndigheten) told Reuters that the probe was regarding millions of kronor. However, she declined to elaborate on what sparked the investigation.
"Prosecutors have taken the decision to look at it more closely. The prosecutor has said it's a matter of millions of crowns. We cannot be more precise than that," the spokeswoman said.
In late February it was revealed that two top Scania bosses made substantial shares purchases in the truckmaker three weeks before majority owner Volkswagen made its take-over bid.
CEO Martin Lundstedt and finance head Jan Ytteberg both snapped up shares reported business daily Dagens Industri. The newspaper calculated that Lundstedt stood to profit by 1.7 million kronor ($266,000) if the takeover bid went through.
Due to their standing and insight into the company's affairs, Lundstedt and Ytterberg must by law report any changes to their shares portfolio to Sweden's Financial Supervisory Authority (Finansinspektionen - FI).
The spokeswoman for the Economic Crime Authority said that the trades done by Lundstedt and Ytteberg were not among the eight cases being investigated.
FI classifies insider trading as something that "most investors associate with illegal conduct. But the term actually includes both legal and illegal conduct.
"The legal version is when corporate insiders buy and sell stock in their own companies. They have a reporting duty and must report their trades to Finansinspektionen," FI states on their website.
Reuters reported that the value of Scania shares rose by more than 30 percent immediately after Volkswagen's takeover bid. The German firm told shareholders that it was willing to pay 200 Swedish kronor ($36.84) per share.
Volkswagen already owns about 89 percent of Scania's voting rights and nearly 63 percent of share capital. The bid is currently being mulled over by the Scania review board.
Scania, which has been in operation since 1891, presently employs 38,600 employees in more than 100 countries. Its headquarters are in Södertälje, Stockholm county, where almost 10,000 of the workforce are based.