Antonietta Sonnessa, lawyer for Ethiopian-born Hamdi Issac, said the questions asked by British authorities "concentrated on the circumstances of the act and the reasons for it."
Sonnessa said a few British officials questioned her client in English, and an Italian magistrate translated. She said Issac replied in Italian.
Britain wants Issac extradited for his alleged role in the botched attack in the Shepherd's Bush subway station last month.
Sonnessa said Issac repeated earlier statements that "it was a demonstrative act and that he knew that the contents of the bag were not aimed to kill."
The lawyer briefed reporters outside Regina Coeli prison some three hours after the British investigators arrived.