Police became aware of a connection between the Rotterdam cell and one led by Trabelsi in Brussels. Trabelsi and a Belgian Moroccan were arrested in two different areas of the Brussels metropolitan area on 13 September in an operation coordinated with the arrests in the Netherlands on the same day. At Trabelsi's apartment, police found machine pistols, chemical formulas for bomb-making, detailed maps of the U.S. embassy in Paris, and a business suit. In a restaurant run by one of Trabelsi's associates, police found materials that could have been used to make a bomb capable of blowing up a building.