Mohammed Mumtaz Tanweer, 56, from Beeston in Leeds, said he and his family were still mystified by his son's motivation.
Mr Tanweer, a Pakistan-born businessman who ran South Leeds Fisheries in Beeston, was speaking after he had taken the remains of his son to Pakistan for burial last week in the family's home village.
The 22-year-old, the first bomber to be buried, killed himself and seven others when he detonated a rucksack bomb at Aldgate station.
Mr Tanweer, in his first interview since the terror attacks, said: "All the bombings and killings were awful. Only the group of four (bombers) or God alone knows why they carried out this terrible act."
He does not know how his son – who looked upon Osama bin Laden as his hero – could have become a terrorist.
"As far as I can understand, my son was more British in his orientation than anything else," said Mr Tanweer. "He has planned his career in sport. Even on the night before he died, he was playing cricket."
He said his son was entitled to a proper burial, although the family now wanted to discover why he carried out the attack.
"My first priority was obviously to bring his dead body to our ancestral graveyard for the burial. Since I'm able to do this only now, I will soon try to find out the reasons (for the suicide mission) and will tell the world."
The remains of Shehzad Tanweer's body were handed over to his parents on Tuesday.
They brought them to a farming village called Chak-477 in Samoondran, a town in southern Punjab, for burial on Thursday.
The dead man's mother, Parveen Akhtar, along with Tanweer's younger brother and his two sisters, "cried uncontrollably" as the remains were taken for final rituals, according to reports.
At least 300 villagers and relatives attended the funeral prayers.
It is not known what will happen to the remains of the other three suicide bombers.
The family of Mohammad Sidique Khan, 30, are understood to be seeking a second post mortem examination on his remains by an independent pathologist.
Khan, who was a teaching assistant in Leeds and the suspected ringleader, carried out the Edgeware Road attack. His family were told last week that they could collect the body parts, which are stored in 50 separate packets.
Shehzad Tanweer travelled to Pakistan last year with Khan and they stayed three months during which time it is thought contact was made with Pakistani extremists .
The British security service MI5 suspects Khan recorded a video message on this visit which was broadcast by al-Jazeera, the Arabic TV station, two months after the attacks.
In it Khan blamed the UK involvement in Iraq for his suicide mission and said: "We are at war and I am a soldier."