After the attacks by Al-Qaeda on the World Trade Centre in New York and other sites on 11 September 2001, the UK Parliament enacted the Anti-terrorism, Crime and Security Act 2001 (ATCSA). Part 4 of the Act allowed the Home Secretary to certify a person as a suspected international terrorist if he reasonably believed that the person's presence in the UK was a threat to national security and reasonably suspected that he or she was an international terrorist. If the person was subject to UK immigration control (i.e., had no right of abode in the UK, not being a British national), he or she could be removed from the UK and detained pending removal under immigration legislation. If a practical consideration (such as the absence of transport links between UK and the place to which the person could be removed) or a point of law which wholly or partly related to an international agreement (for example, where removing a person to his or her country of origin would render him or her liable to torture contrary to Article 3 of the European Convention for the Protection of Human Rights and Fundamental Freedoms (ECHR)) prevented a person's removal or departure temporarily or indefinitely, the Act permitted their detention.