The wife of murdered Pakistani politician Imran Farooq has made a tearful appeal for witnesses to come forward with information about his death. Farooq was killed in London last week. British police say they are keeping an open mind about the motive for the killing.

"Today I want to make my own personal appeal for help in catching the people who killed my husband Dr. Imran Farooq," said Shumaila Imran, the widow of Farooq.

Fifty-year-old Farooq was killed in London last week. He was a leading politician in Pakistan's Muttahida Quami Movement, or MQM, which is part of the ruling coalition in Karachi's Sindh province and the federal government. His death has sparked unrest in the Pakistan city Karachi.

His wife said Thursday that his death has devastated his family. She described him as a loving father and husband and called for any witnesses to come forward.

"It does not matter how insignificant this information may seem to you. It could be absolutely vital to the police investigation," Imran said.

A counter-terrorism unit in Britain's police force has taken over investigation of the case, a sign that police believe the murder was politically motivated.

Detective Chief Superintendent Neil Basu said detectives are doing all they can to catch those responsible.  

"Detectives investigating the attack are keeping an open mind as to the motive behind this attack," Basu said.

Farooq was stabbed and beaten near his home in north London last Thursday. He had been living in Britain and had claimed asylum in 1999 after Pakistani authorities accused him of various crimes.  He denied the allegations.

Farooq's party, MQM, has declared a ten-day mourning period to mark his death.