Hashem Abedi, the younger brother of Manchester bomber Salman Abedi, will be tried in Libya over his suspected role in the attack.
The 20-year-old was arrested in Libya shortly after the suicide attack in May that killed 22 people.
Libya’s chief investigator in the case, Asadiq al-Sour, said Mr Abedi is suspected of having helped his brother and collected materials for the attack. Their father Ramadan, who was also detained in Libya, has been freed.
Hashem Abedi will be taken to court within two months at most.
Libya currently has two rival governments – Mr Sour works for the one backed by the UN, based in the capital, Tripoli.
The country has been wracked by conflict since a Nato-backed uprising against long-serving ruler Col Muammar Gaddafi in 2011.