The suspicion, which has not been identified by authorities, was the subject of a months-long investigation into alleged white supremacist activity, and had recently come with threats the FBI took seriously, the sources said.
Among the threats was an attack on a hospital in Kansas City, Missouri, the area where he lived, in part because of the belief that patients could be treated there for the Covid-19 virus.
It is not clear why FBI agents opened fire during the attempted arrest of the suspect during what was supposed to be a controlled operation in Belton, Missouri. In stabbing operations like Tuesday, investigators typically use undercover agents or informants to gather direct evidence to prove that a suspect was actively planning an attack.
The FBI acknowledged the shooting and the man's death, but declined to provide further information.
"The FBI takes every shooting episode involving our agents seriously," FBI spokeswoman Bridget Patton said in a statement. "In accordance with the FBI's policy, the shootings will be investigated by the FBI's Inspection Division. The review process is thorough and objective and conducted as quickly as possible under the circumstances."
The FBI and the Department of Justice have increased their focus in recent months on racially motivated crimes and threats from white supremacists and other domestic groups, and there are a number of other ongoing federal investigations related to extremists and coronaviruses, one person familiar with the Missouri investigation said.
Internal reports from the Department of Homeland Security and the FBI in recent days have warned of the threat posed by white supremacists and other extremist groups related to the Covid-19 pandemic.
In a DHS document dated Monday and obtained by CNN, the terrorist authorities from the agency cited reports of white supremacists asking people with the virus to intentionally spread it in various neighborhoods and places of worship.
A separate internal report prepared by FBI officials in New York last week also warned of potential efforts by extremist groups to carry the virus against police and Jews.
The report, reviewed by CNN, says: "Members of extremist groups encourage each other to spread the virus, if combined, to target groups through bodily fluids and personal interactions."
On Tuesday, Attorney General Jeffrey Rosen told prosecutors in a memo that they should consider using terrorist actions in cases where certain threats related to the virus were made, including another's targeted exposure and infection.
"Because coronaviruses appear to meet the statutory definition of a & # 39; biological agent & # 39 ;, Rosen wrote, & # 39; such actions could potentially implicate the Nation's terror-related statutes. & # 39;
"Threats or attempts to use COVID-19 as weapons against Americans will not be tolerated," Rosen wrote.
CNN's Zachary Cohen contributed to this report.