Three people arrested last week in connection with the suicide bombings in 2005 on LondonÂ’s transport system, including the widow of ringleader Mohammad Sidique Khan, have been released without charge, police said. A fourth man, aged 34, who was also arrested last Wednesday remained at a London police station after officers were granted a warrant to detain him until May 21. Police said a 29-year-old woman and two men aged 30 and 22 were released without charge on Tuesday evening. A source familiar with the case had identified the woman as KhanÂ’s widow Hasina Patel. She and the three men were detained on suspicion of the commission, preparation or instigation of acts of terrorism. Three men were charged last month with conspiring with the bombers. Police say a key focus of their investigations is to trace people who may have known what the bombers were planning or provided them with logistical support such as money or accommodation.