Muhammad Ghani U., 34, had been arrested in Salzburg along with an Algerian ISIS fighter called Adel H., 28, after it emerged that he had entered Europe along with two other attackers who blew themselves up in the French capital in November.
Both suspects, who had registered for asylum in Austria, are being held under charges of participating in a terrorist organisation.
According to sources quoted in the UK's Sunday Times newspaper, Muhammad Ghani U. is believed to be a ‘veteran bomb maker' for the Pakistani terrorist organisation Lashkar-e-Taiba.
Lashkar-e-Taiba, one of the biggest and most active terrorists networks in South Asia, claimed responsibility for the Mumbai attack in November 2008, that saw the city bombarded by 12 coordinated shooting and bombing attacks lasting four days.
The bomb maker has reportedly since become part of an ISIS fighting team sent to Europe to carry out further attacks.
He came across the Mediterranean on the same boat as two of the Paris attackers and, along with Adel H., was arrested by Greek authorities who spotted they were using passports thought to be some of the 4000 registered as stolen by ISIS.
However, in October they were released and allowed to continue their journey to central Europe.