Investigators from the Tokyo District Public Prosecutor's Office raided the head offices of NEC Corp. and Toyo Communications Corp., both in Tokyo's Minato Ward, on Wednesday to collect evidence to substantiate charges against four officials at Defense Agency contractors who were arrested Tuesday.The four people, including Hiroaki Shimayama, 60, president of Toyo Communications and a former NEC executive director, were arrested on suspicion of causing 1.46 billion yen in damages to state coffers through illegal equipment deals between the agency and Nico Electronics Co., a wholly owned unit of NEC.Wednesday's raid of NEC was the third by the district prosecutor's office following those on Sept. 4 and Sept. 11, carried out in connection with an alleged breach of trust involving Toyo Communications, officials said. Shortly before 10 a.m., 32 law enforcement officers arrived at NEC's head office and entered the office in two rows through its front gate while uniformed guards kept media people back.In addition to Shimayama, those arrested Tuesday were former Nico President Hiroji Takahashi, 63; NEC Manager Takenori Yanase, 57; and Yoshitaka Aihara, 62, a former Nico director in charge of accounting, the sources said. Nico was found to have overcharged the Defense Agency 1.756 billion yen from fiscal 1990 to fiscal 1995 through the sales of cryptogram decoders, but the four people are suspected of having reduced the refund to 297 million yen in a breach of trust, sources said.The overcharging by Nico was discovered in May 1995 by the agency's procurement headquarters' investigation. The illegal deal on the repayment was struck in June 1995, a few days before Kenichi Ueno, then deputy chief at the procurement office, retired from the agency.