British security service MI5 received an anonymous tip-off that one of the London Bridge attackers was an extremist before an investigation was launched into him in 2015, an inquest has heard.
A senior officer identified only as Witness L told the Old Bailey in London that an informant who specifically asked not to be contacted again had got in touch with the security service.
He said the intelligence "identified an individual called Khuram Butt who was in the right sort of age range and said that he was an extremist".
This information was handed over before MI5 launched an official investigation into Butt in mid-2015. He had come onto their radar in 2014 after being identified as a supporter of banned extremist group al-Muhajiroun.
The service only realised after the London Bridge attack in June 2017 that the information had related to the same person.
Butt, Rachid Redouane, 30, and Youssef Zaghba, 22, killed eight people - including Australians Sara Zelenak, 21, and Kirsty Boden, 28 - and injured 48 more in the van and knife attack on June 3, 2017.
They mowed down pedestrians on London Bridge before stabbing innocent bystanders at random in nearby Borough Market.
Jonathan Hough QC, counsel to the inquests into the victims' deaths, asked Witness L if the public should be concerned that the police and MI5 investigation into Butt was suspended for around a month in February 2016, after a series of terror attacks in mainland Europe.
At this stage it was known that Butt:
- Had expressed the desire to launch a terrorist attack in the UK in 2015
- Was publicly associating with members of al-Muhajiroun
- Had disseminated extremist material
- Was considered a risk of travelling to Syria to fight for Isis.
"I think it reflects the level of resourcing available," Witness L said.
"This and other similarly concerning investigations had to be suspended because there were even more concerning investigations above these."
Giving evidence shielded from public view, the officer, who is head of policy, strategy and capability in MI5's international counter-terrorism branch, said money was not the sole issue.
"Even if we'd asked for more money in November 2015, its ability to transfer into actual experienced investigators by 2016 would simply not be plausible," he said.
Earlier he told the Old Bailey that a post-attack review, carried out by a manager in MI5 with a panel of experts, found the investigation into Khuram Butt was "well and effectively run".
It also said the decisions to temporarily suspend investigations into the 27-year-old due to resourcing pressures in February 2016 and March 2017 were "logical and proportionate in the circumstances".
The other victims were Xavier Thomas, 45, Christine Archibald, 30, Sebastien Belanger, 36, James McMullan, 32, Alexandre Pigeard, 26, and Ignacio Echeverria, 39.