Colleagues of a senior exiled Pakistani opposition politician killed in London said on Friday they feared the murder was political, as his home city of Karachi ground to a halt.
Scotland Yard refused to comment on a possible motive for the killing, but the case has been passed to the force's counter-terrorism command.
Analysts said they were keeping an open mind as to the identity of Farooq's killer. The MQM has long-standing rivalries with ethnic Pashtun and Sindhi parties in Karachi, with political killings often followed by tit-for-tat shootings. It was not clear which Pakistani political force would have the ability to strike on a quiet London street — or why they would want to, given Farooq's relative inactivity of recent years.
In the past, the MQM has been rocked by internecine violence.