The British man who was shot dead after taking four people hostage at a synagogue in Texas had been on the radar of MI5, Sky News understands.
The Security Service began looking into Malik Faisal Akram, 44, in the second half of 2020 to assess whether he posed a security threat, a Whitehall source said.
The suspicion that had been raised about him was related to Islamist terrorism.
He had also been in prison four times, between 1996 and 2012, for a range of offences including violent disorder, harassment and theft, Sky News understands.
The so-called "short-lead investigation" into Akram by MI5, however, concluded that there was no "credible threat to national security at that time", the source said.
It meant that no longer term investigation or further monitoring of Akram, who was from Blackburn in Lancashire, was carried out.
"He never reached the threshold" to justify further investigation, the source said.
The source declined to say how long Akram had been looked into other than to say that the investigation had lasted more than four weeks and either ended in the back half of 2020 or by early 2021.
After the investigation concluded that Akram did not pose a threat at that time, he would have joined the ranks of some 40,000 individuals who have at some point been a subject of interest of MI5.
A "short lead investigation" is a term given for a form of investigative process by MI5 into an individual that comes before a longer term, covert investigation.