German federal prosecutors said Thursday they have taken over the case of a suspected far-right extremist accused of leading online groups that preyed on minors and incited killings, arson and severe acts of self-harm across several countries.

Kai M., who is under 20 and was arrested March 17, remains in pretrial detention and is suspected of acting as a ringleader in two organizations that prosecutors have described as criminal and terrorist groups influenced by far-right ideology.

Authorities allege Kai M. and other members manipulated young people online into committing violent crimes, including inducing a minor in Russia to fatally stab another child at a school.

The suspect is also accused of calling for the killing of a U.S. citizen in an online chat and influencing young people in the U.S. and Sweden to set vehicles on fire.

In another case cited by prosecutors, Kai M. allegedly contacted a child in another European country online and coerced the victim into performing sexual acts involving a knife, resulting in serious injuries.