Police in Ostrobothnia suspect a man of slaughtering as many as 1,300 sheep without stunning them first, in breach of Finnish animal welfare laws.
Yle has learned that the suspected crimes took place over four years in the production of halal meat.
Finnish law states that animals must be sedated before slaughter. However, the act does provide an exception for religiously slaughtered animals that are sedated at the same time as bloodletting begins.
The law also states that an inspection veterinarian must be present during the procedure.
According to the Finnish Food Authority, the killing or slaughter of animals in Finland "must be carried out as quickly as possible and in the least painful manner."
In some countries halal slaughter takes place when the carotid arteries of the animal are opened while it is still conscious. This method is against Finland's Protections Act.
Detective Inspector Sakari Palomäki told Yle that the police believe the Ostrobothnian man did not slaughter his sheep in accordance with the law.
"The main suspect lives in the region of the Ostrobothnian Police Department. Most of the suspected crimes have taken place here, but they have also taken place elsewhere in Finland," Palomäki said.
"Planned and repeated" crimes
Palomäki added that the main suspect in the case is not a sheep farmer and has no other related business. Instead, he is suspected of buying sheep in the name of another man and slaughtering them illegally for sale.
"In our view, the activities have been planned and repeated," Palomäki said.
Police launched a preliminary probe after the suspicions were brought to light by animal welfare authorities. The probe began about six months ago and will last for at least another month.
In addition to a serious animal welfare offences, the case is also being investigated for environmental damage as police suspect the slaughterhouse waste was not disposed of in a proper manner.
The suspect had been detained for about one month, but has since been released. Police estimate the suspect may have earned tens of thousands or even more than one hundred thousand euros from the suspected crimes.
Four other people have also been arrested during the course of the preliminary investigation.
An aggravated animal welfare offence is punishable by a minimum of four months and a maximum of four years' imprisonment.