The Stockholm-based gang "Dödspatrullen" (roughly, Death Patrol) organised the smuggling of hundreds of kilogrammes of illegal drugs into the Finland, according to Finnish news agency STT.
Finland's National Bureau of Investigation and the Helsinki Police Department have worked on the case with Swedish authorities, and their probe is nearing completion, STT reported.
The suspected crimes were allegedly carried out between June 2022 and May 2023.
According to STT, Swedish police tipped off Finnish authorities with an address in Finland that led to the discovery of a suspected drug distribution operation.
Police suspect that the drugs were brought to Finland in trucks via the northern border, STT reported, citing several sources. Authorities have seized more than 100 kilogrammes of drugs.
The suspects involved in the case range in age from 21 to 25, all four of whom were remanded in custody in absentia at the end of May. STT reported that three of the suspects have since been extradited to Finland.
According to authorities the investigation is also linked to the seizure of a large number of weapons in Sweden last spring. The tabloid Aftonbladet reported in April that Stockholm-area police seized more than 20 firearms during a single operation, likely making it the biggest such raid in years.
Authorities in Sweden have struggled with a major uptick in gang violence in recent times, with more than 10 gang-related deaths last month alone.
The reason for the uptick in violence is thought to be related to inter-gang disputes and competition.
Swedish police told national broadcaster SVT on Monday that authorities are starting a nationwide operation to stop the wave of violence. The effort will include increased inter-agency cooperation as authorities respond to eventual explosions or shootings in the future.
The law enforcement effort will also include help from the Swedish military.