The investigation by federal authorities into the murder of conservative figure Charlie Kirk has yet to find a connection between the suspect, Tyler Robinson, 22, and any left-wing organizations that President Donald Trump and his administration have been targeting since the incident, according to three sources familiar with the investigation, as reported by NBC News.

One person familiar with the federal investigation said that “thus far, there is no evidence connecting the suspect with any left-wing groups.”

“All the evidence currently suggests that this was an act by an individual who reacted violently because he found Kirk’s beliefs offensive,” one source stated.

Additionally, two of the sources indicated that it might be challenging to press federal charges against Robinson in connection with Kirk’s death, although the third source maintains there’s an anticipation for some form of federal accusation against Robinson.

Several factors have complicated the pursuit of federal charges: Robinson resides in Utah and did not cross state lines; furthermore, the shooting occurred during a campus debate event at Utah Valley University, and Kirk was not a federal employee or public servant.

A Justice Department spokesperson said, “The investigation is ongoing and beyond that we decline to comment.”

Robinson is currently facing state charges, which were disclosed on Tuesday. These include aggravated murder and obstruction of justice, amongst others, with Utah prosecutors aiming for the death penalty. Prosecutors allege Robinson targeted Kirk, who co-founded the conservative group Turning Point USA, due to his “political expression.” Robinson’s mother informed investigators that over the past year, he had become more political and began to lean leftwards.

Thomas Brzozowski, who was recently the Department of Justice’s counsel for domestic terrorism, mentioned to NBC News that although Kirk’s murder meets the definition of domestic terrorism, identifying a federal charge might be difficult. There is no specific federal statute criminalizing domestic terrorism, although sentencing enhancements can be sought after conviction.

The FBI is frequently involved in domestic terrorism investigations that ultimately result in only state-level charges.

“As is always the case, the FBI needs a federal hook to initiate an investigation,” Brzozowski said. “Here, it appears that they’re acting in an assistance to state authorities’ capacity.”

Charging documents filed Tuesday also contained a series of texts between Robinson and a roommate, whom police described as “a biological male who was involved in a romantic relationship” with the suspect and transitioning to female. The roommate’s identity has not been made public.

The texts appear to link Robinson to the crime. One message alerted the roommate to a hidden note in their residence, which read: “I had the opportunity to take out Charlie Kirk and I’m going to take it,” according to the documents.

“What?????????????? You’re joking right????” the roommate apparently wrote back.

Robinson allegedly told the roommate he planned the attack for more than a week and, when asked why he killed Kirk, said: “I had enough of his hatred. Some hate can’t be negotiated out.”

Following Kirk’s shocking assassination, which has sparked a wave of grief, fear and fury on the right, Trump and his allies have threatened to come after left-wing advocacy groups that they saw as fomenting the anger that led to Kirk’s death.

Stephen Miller, the White House deputy chief of staff, said left-wing organizations amounted to a “vast domestic terror movement.”

“With God as my witness, we are going to use every resource we have at the Department of Justice, Homeland Security and throughout this government to identify, disrupt, dismantle and destroy these networks and make America safe again for the American people,” Miller said recently. “It will happen, and we will do it in Charlie’s name.”

As NBC News reported Thursday, that effort is likely to face hurdles.

“There’s not a lot of federal law on this,” Scott Walter, president of the Capital Research Center, a Washington-based nonprofit organization that tracks progressive groups and is influential in conservative circles, said then. “Frankly, the states and localities should be doing a better job [of prosecuting criminal activity], as they did in the 1960s. They have enormously more manpower.”

Since 2002, right-wing ideologies have fueled more than 70% of all extremist attacks and domestic terrorism plots in the United States, according to the Anti-Defamation League.

The Justice Department also said in a study last year that the number of far-right attacks in this country continues to outpace all other types of terrorism and domestic violent extremism. The study was removed from the Justice Department website in the past few days, according to 404 Media.

Kirk’s funeral is set for Sunday in Arizona. On Thursday, a joint bulletin authored by the Federal Bureau of Investigation; Secret Service; Bureau of Alcohol, Tobacco, Firearms and Explosives; and the Department of Homeland Security said law enforcement is “tracking several threats of unknown credibility” against people who may be planning to attend Kirk’s memorial, though so far there’s no concrete evidence that anyone is in danger or that the threats are real, according to a senior law enforcement official.