The mix-up occurred last week during a night-time hunt near Hultsfred, The Local.dl reported. The hunt was sponsored by a local landowner who also happened to be the owner of the two dead bulls.
Police were trying to determine whether the Dane violated any Swedish hunting or firearms regulations.
Christer Karlsson, a spokesman for the Kalmar County police, said the two bulls weighed 800 kilograms (1,760 pounds) each while even the heaviest wild boar typically weigh no more than 400 kilograms (440 pounds).
"You think he would be able to see the difference," Karlsson told the newspaper Expressen.
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