The operation was carried out by the investigation section's serious crime group and the regional task force on the occasion of Sunday's shooting in Årby.
They do not want to say what it is about drugs and weapons that the police have found.
They are also silent about how many have been detained and what they are suspected of.
- There are reasons why we can not talk about this more than we have done today, says Christoffer Bohman, head of the investigation section in the Södermanland police area.
Escalated conflict
Since January, four shootings have occurred in Eskilstuna.
Two in the Skiftinge district and two in Årby.
The police link the shootings and they see an escalating conflict between criminal networks in the neighborhoods.
Earlier this year, the police carried out an operation in Årby where they were looking for an object that could be used in violent crimes.