The motive behind Charlie Kirk's killing: What we know and don't know

The roommate of the suspect in the killing of Charlie Kirk had one question.

"Why?"

"I had enough of his hatred," Tyler Robinson wrote back. "Some hate can't be negotiated out."

On Tuesday, authorities released messages between Robinson and the roommate from the hours after the shooting. Officials have said the unnamed roommate was a "biological male" who was transitioning from man to woman and was in a romantic relationship with the defendant.

Prosecutors also gave further details that could point to a possible motive – although there is still much that is not known.

According to an indictment, Robinson's mother told police that over the last year or so, Robinson had become more political and left-wing, "more pro-gay and trans-rights oriented".

And in family conversations before the shooting, Robinson allegedly accused Kirk of spreading hate.

Prosecutors say Robinson left a message for his roommate: "I had the opportunity to take out Charlie Kirk and I'm going to take it."

During Tuesday's news conference, Utah County prosecutor Jeff Gray said instead of deleting the messages like Robinson asked, the roommate provided the missives to police.

The messages and interviews with family members form crucial parts of the indictment against Robinson and give some insight as to his state of mind.

In addition, investigators have also said that four shell casings were found alongside a rifle discovered in a wooded area near the Utah Valley University campus.

The shell casings had messages engraved in them which, prior to Robinson's arrest, were among the only potential clues as to the killer's motive - and have been the subject of much speculation.

One unfired round had the words "Hey fascist! Catch!" along with an up, right and three down arrows – mostly likely a reference to a video game, Helldivers 2, indicating one of the game's special moves.

Another shell casing, authorities say, read "NoTices Bulge OWO What's This?" - a reference to a meme about furry subculture and online roleplaying.

The BBC has also seen an online profile allegedly owned by Robinson on a website dedicated to furry fandom, suggesting he may have had an interest in the subject.

Another casing was inscribed with lyrics from the song Bella Ciao, which honours World War Two-era partisans of the Italian resistance who fought Nazi Germany. The song has also appeared in a video game, a TV series and has been covered and remixed many times in the years since.

The fourth cartridge read: "If you Read This, You Are GAY Lmao" – another online reference.

But the exact meaning of the messages, if indeed they are intended to have any meaning at all beyond a prank, is still unclear. The nature of online language, with its layers upon layers of irony, means that multiple interpretations are possible.

In the messages to his roommate Robinson said the engravings were "mostly a big meme", indicating perhaps that they should not be taken as a serious statement.

Pictures of social media accounts apparently owned by Robinson and his roommate which have been circulating online are mostly focused on gaming - it appears that both Robinson and his roommate were keen video gamers.

The accounts do include a few scattered comments on politics, none of them particularly conclusive or directly indicative of a motive. The BBC has reviewed the accounts, but has not been able to confirm that they belong to the pair.

According to the messages released by prosecutors, when asked by his roommate how long he'd taken to plan the attack, Robinson responded: "A bit over a week."

• Read the text messages between Charlie Kirk accused and roommate

Prosecutors in Utah mostly declined to answer questions from the media on Tuesday, and although the state's Governor Spencer Cox said Robinson had a "leftist ideology", there are still gaps in what we know about a possible motive.

For instance, it's unclear what specifically Robinson found objectionable about Kirk. It's also unclear how Robinson might have been radicalised and what role his online activities might have had in that process.

Authorities have been tight-lipped about what role - if any - the suspect's politics played in the attack.

When Grey, the county prosecutor, was asked directly whether transgender activism inspired the shooting, he declined to comment.

There also remains the possibility that the suspect may have had no coherent political stance. In several recent US mass shootings and assassination attempts - including the attempted assassination of Donald Trump in Pennsylvania last July - killers have appeared to have a jumbled set of political beliefs, or no clearly defined ideology.

The FBI recently recognised a new category of threat called nihilistic violent extremism or NVE, defined by a general hostility to society and desire for chaos rather than a sharply defined ideology.

FBI Director Kash Patel said in a Senate hearing Tuesday that his agency had seen a large uptick in cases involving NVE.

In the Kirk case, Katherine Schweit, a former FBI agent and prosecutor, said investigators will be busy tracking Robinson's online communications and interactions with friends and family members to glean more information.

"That gives us a lot of insight into somebody's pathway to the violence," she said, adding that agents will "piece them all together to see how someone moves on the pathway from frustration all the way to choosing to commit a violent act."

The prospect of capital punishment means that prosecutors will need to show intent to commit murder when they press their case in court. However, Schweit says that's distinct from motivation, which may or may not be directly relevant to the case.

"TV and movies have taught us that the motive is the most important thing, but from a prosecution standpoint, it's not."

Schweit also noted that some high-profile assassins have been motivated by the desire to be famous or impress people.

• Charlie Kirk suspect confessed in note to roommate, prosecutors allege
• Who is Tyler Robinson, the suspect in custody for shooting Charlie Kirk?
• Kirk shooting throws Utah students into heart of US political divide

During Tuesday's Senate hearing, FBI director Patel also said that others are being investigated for possible involvement in the shooting.

As of yet, no-one else has been charged in connection with the case and investigators have not indicated anyone else was involved.

That has not stopped fevered - and for the most part un-evidenced - speculation online about alleged motives and large-scale plots.

A number of right-wing influencers with huge social media followings, including several who are close to President Trump and Kirk's Turning Point USA organisation, have alleged that the shooting was the work of a group or "terror cell" inspired by transgender activism and funded by left-wing activists.

Trump said this week he will designate Antifa as a "major terrorist organisation" as part of his efforts to target the "radical left", following Kirk's killing. Robinson, the suspect, has not been directly linked to Antifa, a decentralised, leftist movement that opposes far-right, racist and fascist groups.

• What is Antifa and why is Trump targeting it?

Some high-profile right-wing podcasters, including Trump's former chief adviser Steve Bannon, have suggested that the text messages exchanged by Robinson and his roommate were somehow faked or false, implying - again without evidence - a broader conspiracy.

At the same time, a number of left-wing social media users have continued to claim that Robinson is a Trump supporter or member of a fringe, far-right group known as "groypers" - who consistently castigated Kirk for not supporting their white nationalist and anti-Semitic beliefs.

Those claims also lack evidence, and prosecutors and Utah officials have given no indication that far-right groups are involved.

"Everybody's jumping to conclusions because that's the society we live in," said Schweit, the former FBI agent. "Everybody wants an answer – and right now."