The Hamara youth access centre in Lodge Lane, Beeston, does not look like a seat of jihadist fundamentalism. It closed last December when its services were moved to a custom-built centre in the next street, and has since been empty and derelict.
But in the eight intervening months, it is known to have become a meeting place for Muslim youths. They may have fallen under the influence of a number of individuals. Several of the identified suicide bombers from last Thursday are known to have visited the property.
Critical to police inquiries about the centre's part in nurturing fundamentalism is the evidence provided by a youth worker who remained under arrest at Paddington Green police station in west London last night, after police secured an extra three days to question him.
Some sources suggest the investigation in Leeds is now being driven by the information that the man, aged 29, is providing.
Detectives are also examining suggestions that a senior agitator named by a source in Beeston as "Mr Khan" and by other sources as "Mr K " may have played a part in recruiting and radicalising the three young men. He is not be confused with Mohammed Sidique Khan, one of the bombers, who was responsible for the attack on the Tube train at Edgware Road.
The Beeston source said that a "Mr K" was well known to the Fiaz family and had also become a key influence in the life of Hasib Hussain, the 18-year-old Tavistock Square bus bomber. The source said Hussain's father, Mahmoud, was distressed by Mr Khan's influence on his son. Mahmoud Hussain recently told the source his son had become radicalised under Mr Khan's influence. As a result of his influence, Hasib had developed "two religions," the father had said "Muslim and another kind of Muslim".
Other sources confirm the name "Mr K" kept cropping up. He was a domineering figure known to the bombers who has settled in Leeds from Pakistan where he is said to have had a background as a preacher.
Police threw a 100-metre cordon around the Hamara youth access centre yesterday, as their investigations into its activities proceeded. In the afternoon, the bomb squad used a robotic arm to lift the shutters which have been pulled down on the premises since the police's attention turned to Leeds.
Bomb disposal experts could then be seen shining a torch inside. One family friend of the man under arrest said he had been an influential figure at the centre. "He was always in the youth club. He would open the shop and we would see him close up," she said.
Police arrested the man during the dawn raids in south Leeds and Dewsbury three days ago.
Another resident in Beeston said the identified bombers used to work in the youth centre. He said: "All the young Asians used to congregate near the mosque and near the project centre. It used to be two houses which were knocked into one. It was recently closed down and moved to another area."
But the youth centre, run in partnership with the Leeds Community School in Lodge Lane, is not the only place where the bombers might have met to formulate their ideas.
The Stratford Street mosque, which at least two of them regularly attended, is no hotbed of radicalism, judging by many interviews with those who worship there. But the road outside the mosque is an informal social centre for young worshippers from Beeston and neighbouring districts such as Holbeck (Hussain's neighbourhood) where there are no mosques.
Simple leafleting campaigns may also have helped draw the three to radicalism, according to one Muslim who worships at Stratford Street. " Al-Mujaharoun [the hardline Islamic organisation] and others regularly leaflet in barbers shops and corner shops around here for meetings up at Bradford, Dewsbury and Huddersfield," he said.
That introduction to radical Islam may have, in effect, "created" the individuals that the more senior agitator was seeking to exploit for his deadly plot. In a day of high drama in Beeston, dozens more homes were evacuated when the security cordon was extended to encompass the largest area since Tuesday.
A spokesman for the British Red Cross said it was setting up a facility in Leeds for up to 200 people following the operation in Beeston. He said a "rest centre" was being opened at the South Leeds Sports Centre and would be available "for as long as it takes".
The spokesman said as well as providing food and other necessities, staff would be on hand to lend "emotional comfort and support for people facing a very difficult situation".
Police attention also continued to focus on a flat at Alexandra Grove, in the Burley district of Leeds, where police found a bath filled with explosives.
That property also holds clues about the people who the would-be bombers were introduced to. Samir Al-Ani, in his mid-40s, lived there during a brief stay before going to Iraq two months ago. However, police sources and the security agencies stress that there is no evidence he was the bomb-maker.
Also involved with the flat was Magdi Elnashar, an Egyptian PhD student in biotechnology. Again, the police stress that Mr Elnashar is neither a suspect, nor a part of their investigation.
Shakir Al-Ani, a relation of Samir Al-Ani, recalls a telephone call from Mr Elnashar who said a "friend" from London needed somewhere to stay and asked whether the ground floor flat at Alexandra Grove was available.
Shakir Al-Ani said the man subsequently moved into the flat and wanted to move some of the furniture because he "needed some space". Later, Mr Al-Ani says, he received a call from Imran Hussain, Hasib Hussain's brother, asking why Mr Al-Ani's telephone number was in his brother's mobile telephone.
Mr Al-Ani says he had no explanation for the appearance of his number on the phone of the young man who detonated a bomb on the No.30 bus just outside the BMA's headquarters.