Violence fears in Pakistan after Imran Farooq's murder
"This is the most tragic event in the history of our party", says a red-eyed Farooq Sattar.
Mr Sattar is head of the MQM's leadership in Pakistan. He was speaking to the BBC in a small crowded room in the ancestral home of the now-deceased Imran Farooq.
Sitting beside him is a frail and weary looking Farooq Ahmed - father of the slain MQM leader.
We had arrived a little earlier at the Farooq residence in Karachi's middle-class neighbourhood of Sharifabad. Located near the heart of the city, it is made up of apartment complexes - and small three-storey houses. The Farooq residence is just such a building.
Hundreds of grim-looking mourners are packed into the narrow lanes leading up to the house.
There is also a great deal of anger, although it has been muted so far.
Security is tight - there is a strong presence of paramilitary rangers and police.
MQM activists have also set up several checkpoints where all cars and pedestrians are thoroughly searched.
We have just driven down from the nearby MQM party headquarters. There were fewer people there, but just as tight security.
The party leadership in Pakistan is now debating what should be their future strategy.
'Cause not accomplished'
Despite the fact the murder took place thousands of miles away, there is real fear here.
After many years of relative calm, it appears the MQM is once again feeling under siege.
"I spoke to my son a day before the incident - he was fine and spoke cheerfully," Mr Ahmed says.
Sitting on a bed across from him is his wife Raeesa, who breaks out in tears at the mention of her dead son's name.
"My boy was a good man - he only fought for the poor and underprivileged," she says.
"I was so afraid for him when the operation started - but was happy when he appeared in London.
"Even though he was so far away, at least he was safe."
Both parents say the last time they saw their son was back in May 2009.
"He was happy with life and committed to his work in the party," his father says. "On Wednesday, he was telling me how his children were doing - he was quite pleased."
However, he refrained from commenting who might be behind the murder: "I can't say who was responsible."
He does add something rather cryptically.
"The situation is still the same, " Mr Ahmed says, referring to MQM's struggle against he country's status quo. "The cause for which he was fighting has not been accomplished. Being in the government was never the goal."
His mother, however, breaks down in tears again.
"He was a patient, humble boy - he was always worried about my health," she says.
Outside, neighbours and well-wishers express similar sentiments.
"He was a quiet and well-behaved young man," says Faiz Mohammad, an elderly man. "I remember meeting him in the streets and he was always very polite. The charges against him were all rubbish - the army manufactured them to malign him."
Ruksana, a young woman who was amongst the mourners, says that "Farooq was an inspirational leader".
"We want to say to Altaf Altaf Hussein [MQM leader], we are with you and you should not feel alone," she adds.
Meanwhile, emotions continue to simmer as some MQM leaders say there could be trouble if a connection to the killing is established with Pakistan.
"Our leaders continue to be killed despite the restraint we have exercised," says deputy parliamentary leader Faisal Subzwari. "We are committed to the peace in Pakistan, but some forces have not accepted our anti-feudal policies and continue to target our leaders."
Despite such provocations, Mr Subzwari says the MQM has shown great restraint.
But if links are established between Pakistan and Mr Farooq's assassin, that may be soon be swept away.
For Karachi, and Pakistan, the consequences are terrifying.