Known as Kaka, a nickname he acquired as a child, he was devoutly Muslim and would "salaam" to every passer-by in the Asian community in Beeston, but would not make eye contact with women, a practice among strict Muslims.
He was the second oldest of four children and the son of a successful businessman, Mohammed Tanweer, who runs a chip shop and owns a halal slaughter house. He and his siblings, all of whom are unmarried, attended Wartley School in Leeds. Punjabi and English were spoken at the family home.
In December 2004 Tanweer travelled to Pakistan for a course in Islamic studies, but returned earlier than planned. His uncle Bashir Ahmad, a businessman who runs a kebab takeaway shop, said: "It was supposed to be for nine months but he came back after two months. He said he did not like it because those people in Pakistan did not respect people coming from England."
After returning from Lahore in February, he worked full time at his father's chip shop and was considered a friendly, if private, figure by customers. His father, Mohammed, who is in his mid-fifties, came to England from Faisalabad, Pakistan, about 20 years ago. Shahzad's mother, regularly sewed traditional Asian clothes for money at home, and Mr Tanweer, who was well- educated, helped people with paperwork.
Shahzad was born in Britain and was seen in both Asian and Western clothes. Most days he would wear a designer tracksuit with trainers but also wore traditional Asian dress.
He had a small beard but went through phases of shaving it off and growing his hair to a length similar to the prophet Mohamed, according to his uncle, Mr Ahmad. He added: "He could not make up his mind what he wanted to be. He had a beard one day and not another. He grew his hair long, but everyone in Pakistan stared, so he had it chopped off."
His sister Tabasum, believed to be 24, went to university and is the manager of a local shoe shop. His second sister, Tilet, believed to be 19, also went to university, and his youngest brother, whose nickname is Nicky, believed to be 18, is studying at college.
According to a family friend, Shaziyah Khan, 25, who has known the family since childhood, Shahzad was a devout Muslim, observing five prayers a day and having taken the pilgrimage to Saudia Arabia known as the Haj.
The family owns property in the Beeston area of Leeds. Mr Ahmad said Shahzad had a passion for sport, especially cricket, and would spend hours talking about the game, but never discussed politics. Mr Ahmad believed Shahzad had begun a degree course at Leeds University, but dropped out. "The news is just unbelievable," he said. "It's very hard for me to believe Shahzad could do anything like that.
"When I came to England 10 years ago, I lived with Tanweer and his family for a long time. I saw the children when they were young and used to play with them. I cannot believe Shahzad did this because I can't believe he's capable of it."
Nusrut Hussain, a mother who lives five minutes away from Colwyn Road, was best friends with Shahzad's sister Tabasum for many years, and said she had sympathy for the Tanweer family. "I just cannot believe anyone in this family could do any wrong. My mum lives on the same street, we grew up playing together and going to each other's houses.
"The father is extremely well respected in the neighbourhood."
Rashid Facha: Married man who rarely acknowledges others
In his late 20s and of Pakistani extraction, a neighbour said of Mr Facha: "He has not been seen since last Thursday. He is married to a local Hindu girl.
"She is the daughter of a retired and a recently widowed high-school teacher, who is a highly respected member of the local community.
"The Fachas have an eight-month-old daughter. Mr Facha has a low profile on Lees Holm - a cul-de-sac of semi-detached red brick houses 10 miles east of Leeds - and rarely offers more than a cursory hello or goodbye.
"He is known to have worked out regularly at a local gym and has been seen leaving his home with a kit bag over his shoulder."
Hasib Hussain: A troubled adolescent who turned to religion
Leeds born and bred, the younger of two brothers raised by a factory charge hand, and his wife.
He has had a troubled adolescence and is said by neighbours to have gone "off the rails."
Locals said that his parents had tried to discipline him but he had turned to religion 18 months to two years ago and had become devout.
He is believed to have gone to London last week and has not been seen since.
His brother has been ringing him but has had no reply, leading his parents to report him missing to police.
The first British suicide attackers
The first known British suicide bombers were Asif Hanif, who was 21, from Hounslow, south-west London, and Omar Khan Sharif, 27, from Derby, who launched a suicide attack at a bar in Tel Aviv on 30 April 2003.
They sought to justify the lethal attack which they were about to make in a videotape in which they were seen rejoicing at the prospect of killing Israelis. The pair had joined the militant Palestinian organisation Hamas.
Hanif says: "What can I say? The real terrorists are these Israelis. They're really sickos... Muslims are being killed every day."
They killed three people, two musicians and a waitress, and injured 65. Hanif died at the scene after the device strapped to his body exploded. Sharif's explosives failed to detonate and he fled.
His body was found 12 days later in the sea. Sharif and Hanif had used their British documents to travel to Israel.
Neither man had any criminal record, though intelligence agencies had monitored them attending meetings staged by the extremist al-Muhajiroun group, which has praised Osama bin Laden and the hijackers who carried out the 11 September attacks.
Sheikh Omar Bakri Muhammad, al-Muhajiroun's founder who gave religious instruction to the bombers, said they "died on the battlefield and will now go to paradise".
Sharif was married with two children. Tahira Tabassum, Sharif's widow, was found not guilty of failing to alert authorities to the intended terrorist act in July 2004.
She told the Old Bailey she thought her husband intended to leave her. But Zahid and Parveen Hanif, Asif's brother and sister, face retrail.
The video showing them talking about their motivations for killing was undeniably shocking. The British passports the suicide bombers carried amplified the sense of horror.
Genevieve RobertsReuse content