A Vaud cantonal police car ran over the victim at around 2am on Thursday as he was lying on the road near an interchange in Bussy in the canton of Fribourg, close to the Vaud border, according to a Vaud police news release.
Officers in the patrol car were responding to a complaint from another 22-year-old man, in the nearby town of Payerne in the canton of Vaud, who phoned at 1.45am to say he had been attacked by someone with an electroshock device.
Prosecutors from the two cantons have opened separate investigations into the bizarre affair, officials said on Tuesday.
At this stage of the investigation, the chief prosecutor and investigators from Fribourg believe the man who died was the victim of an accident, Vaud police said.
Video surveillance cameras recorded other vehicles passing by the site of the incident and police are hoping to speak to motorists who may be able to shed more light on precisely what happened.
The victim was apparently walking home from Payerne to his home in Estavayer-le-Lac in a part of Fribourg that borders Lake Neuchâtel, Vaud police said.
He was found to have a blood alcohol limit of 2.4, almost five times the Swiss legal limit for driving, while results of toxicology tests were not yet known, police said.
The victim and the man who contacted police to complain of being assaulted knew each other and spent Wednesday night drinking in bars and in an apartment in Payerne where they met several people, Vaud police said.
Investigators want to speak with anyone who may have seen the men on that night, in particular, a man and a woman who were in their company at the apartment, police said.