One of the men involved in last Saturday's London Bridge attack tried to rent a larger truck that could have killed more people, but his payment was declined, police say.

In a rare glimpse into the weeklong investigation, police have released further details about the attack, including the fact that Khuram Butt originally tried to rent a 7.5-tonne truck. It would have been smaller but similar to the 19-tonne truck driven into crowds last July in Nice, France, killing 86 people and injuring hundreds.

Eight people were killed, including Christine Archibald, a Canadian, and dozens more injured in Saturday's attack on London.

After his payment was declined, Butt and his two accomplices rented a small van that they used to plow into crowds on London Bridge before they leapt from the vehicle and went on a stabbing rampage. They used 30-centimetre knives with bright pink blades, according to Dean Haydon, head of the Metropolitan Police's Counterterrorism Command.

Gasoline bombs in van

In a statement released late Friday night local time, police also disclosed that multiple Molotov cocktails were discovered in the van, and a copy of the Qur'an opened at a page "describing martyrdom" was found at one of the attackers' houses.

Investigators believe three victims were killed on the bridge, including one man who was thrown into the Thames River, before the attackers left the vehicle and stabbed five people to death around London's busy Borough Market, Haydon said. Police believe Butt was driving the van.

"When I come back to Butt trying getting hold of a 7.5-tonne lorry — the effect could have been even worse," he said.

People gather for a vigil in Potters Fields Park in London on June 5 to commemorate the victims of the attack on London Bridge and at Borough Market. (Daniel Leal-Olivas/AFP/Getty Images)

More than a dozen wine bottles filled with flammable liquid and rags wrapped around them in the shape of Molotov cocktails were found in the van. Two blowtorches were also found.

Haydon said the men may have been planning even more bloodshed if they had survived their stabbing spree and made it back to the van.

Police also found a number of office chairs, gravel and a suitcase in the van.

Detectives believe the gravel may have been placed in the vehicle to make it heavier, or as part of a cover to justify hiring it, while the chairs may have been used to convince family and friends they were moving furniture.

Butt, a 27-year-old Pakistan-born British citizen, and his two accomplices, Rachid Redouane, 30, who claimed to be Moroccan-Libyan, and Youssef Zaghba, a 22-year-old Italian national of Moroccan descent, were shot dead by armed police eight minutes after the first emergency call.

The three attackers were wearing fake suicide belts consisting of plastic water bottles wrapped in grey duct tape.

Haydon described the pink knives as "pretty unusual" and appealed for anyone with information about where they came from to contact police.

Appeal for information on knives used in <a href="https://twitter.com/hashtag/LondonBridge?src=hash">#LondonBridge</a> terrorist attack <a href="https://t.co/AlGeo1gtit">https://t.co/AlGeo1gtit</a> <a href="https://t.co/K6QSSXOE06">pic.twitter.com/K6QSSXOE06</a> —@metpoliceuk

Police raided Redouane's small residence on Tuesday and said he had been renting it since April. This was the safe house where the attack was planned, police said.

In the residence, police found the English-language copy of the Qur'an opened at a page describing martyrdom, as well as pieces of cloth which appeared to match the material wrapped around the Molotov cocktails and water bottles similar to those used in the fake suicide vests, police said. Luggage straps, plastic retractable craft knives and rolls of duct tape were also found.

Eighteen people have been arrested in connection with last week's attack. All but five have been released. Searches are continuing.

Wider plot not suspected

The question remains how the men met and knew one another, but police said they did not suspect a wider plot.

"It looks as if it is pretty much a contained plot involving the three of them, which is supported by the forensic evidence we've got back so far," Haydon said.

Butt, who police consider the attack ringleader, had been on bail after being arrested for fraud in a case in October of last year, police said. He had also been repeatedly reported to police for violent behaviour and trying to recruit young children to ISIS. He was featured in the documentary The Jihadis Next Door, where he was seen next to a group of men unfurling a black-and-white flag scrawled with Arabic script and associated with ISIS.

"There was no evidence uncovered of any attack planning in relation to him," Haydon said.

Butt had been warned by police on two occasions — once for fraud in 2008 and once in 2010 for assault. Still, he did not have any criminal convictions.

Zaghba and Redouane lacked any criminal convictions or such warnings in Britain.

"From what I'm seeing, there is nothing that suggests at the moment that we got that wrong," Haydon said, referring to Butt.