In the Saturday night rampage, the attackers first drove a rented van into a crowd and then jumped out and randomly stabbed people they encountered.
In the documentary, Butt appears in one of the key scenes with others from the group angrily arguing with a police officer after they have displayed the flag used by IS in one of London's parks.
The youngest of the attackers, an Italian national of Moroccan descent, he was allowed to enter the United Kingdom and had been living in east London.
Both British authorities and Ireland's Police Commissioner Noirin O'Sullivan have said they had no evidence Redouane was involved in any terror cell during his time in both countries.
Meanwhile, a man has been arrested on suspicion of terror offences by detectives investigating the London Bridge attack following an early morning raid at an address in east London.
The death toll from the London Bridge terror attack has risen to eight after police searching for a French man missing since Saturday recovered a body from the River Thames. Seven were killed and almost 50 wounded. He was known to security services and had appeared in a televisions documentary "The Jihadis Next Door", which was broadcast past year.
The Metropolitan Police says an area near the building was cordoned off as officers investigated the vehicles in Vauxhall. Zaghba's father is said to be in Morocco.
AFP has compiled what is known about the three men, amid an ongoing investigation into the third deadly jihadist assault in Britain claimed by the Islamic State group in less than three months. They returned the device but pointed him out to London as a possible suspect, Amato said. Ireland's national broadcaster RTE reported that Redouane had an Irish residency card and had lived in Dublin.
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As a holder of an Italian passport Zaghba was not liable for expulsion under the kind of administrative order Italy routinely uses against suspected Islamist militants from Morocco and Tunisia.
Less than two weeks earlier, a suicide bomber had killed 22 adults and children at a pop concert in Manchester and, in March, five people died after a vehicle was driven into pedestrians on London's Westminster Bridge.
Zaghba, a 22-year-old with dual Moroccan-Italian nationality, was briefly detained after being stopped at the airport in Bologna, central Italy in March 2016.
When he was stopped at Bologna airport, the woman begged police not to let him leave because she was anxious about "strange" talk from him.
"Last year. when I went to England, he was a bit more rigid", Collina, a convert to Islam, told reporters in a series of interviews Wednesday.
Liberal Democrat leader Tim Farron added his voice to the chorus, saying that, in her former role and now as Prime Minister, May had "shown contempt for our police force". A string of opinion polls over the past couple of weeks have pointed to a narrowing in the gap between her Conservative Party and the main opposition Labour Party. "However, there was no intelligence to suggest that this attack was being planned and the investigation had been prioritized accordingly", he said. Between 2009 and 2016, the number of police officers fell by nearly 20,000, or around 14 percent, according to the independent Institute for Fiscal Studies think tank.
"It is seeking to project its influence and maintain its relevance by inspiring, encouraging, and - though there does not appear to be evidence of this in the latest United Kingdom plots to date - directing attacks in Europe and elsewhere", he said.
Associated Press writers Paisley Dodds and Raphael Satter reported this story in London and AP writer Kathy Gannon reported from Pakistan.