Do you know why gangs form? It’s much closer related to poverty and other systemic issues, than who the people themselves are. Being a gangster is not something that’s in your genes, it’s formed from environmental factors. Gangs come into existence because the system fails them, and they fall through the cracks.
When someone immigrates its likely due to a strong need to do so. And if you’re new to a country, you won’t know anyone, or have a solid grasp on the language, have little money, and likely struggle to find a job. These are the factors that cause criminal activity. They require active intervention to handle. And, very coincidentally, Sweden has been defunding or privatizing a lot of its public welfare state in recent times.
For example, someone being lonely and unable to find a job is a prime target for bad stuff. This is the target demographic of the alt-right pipeline, for example. Which also, by the way, very much is a thing that operates on non-immigrants too, it’s just that they tend to go through politics, removing the rights of others, bigotry in politics, or move towards a police state.
It’s short sighted to look at these problems as some individual failings, instead of the systemic issues that they are.