As investigators pore through online messages, notes and engraved shell casings in their search for a motive in the killing of one of the country?s most prominent conservative activists at a Utah Valley University campus event, authorities are also looking into whether suspect Tyler Robinson?s romantic relationship with a transitioning roommate was a factor in the shooting, Utah Gov. Spencer Cox told CNN?s Dana Bash on Sunday.

Meanwhile, mourners across the country are attending vigils to pay tribute to Charlie Kirk, a 31-year-old ally of President Donald Trump and cofounder of the youth organization Turning Point USA.

The 63,400-seat State Farm Stadium in Glendale, Arizona, is preparing to host a massive memorial the morning of September 21 that is expected to be a testament to Kirk?s influence. His widow, Erika Kirk, pledged Friday to continue his work, including his campus tours and podcast.

Here?s what we know about the investigation into the killing and how Kirk is being mourned.

What charges does the suspect face?

Robinson is set to appear in court Tuesday, accused of killing Kirk. He is being held without bail at Utah County Jail on charges including aggravated murder, felony discharge of a firearm and obstruction of justice, according to officials. Utah Attorney General Derek Brown would not say Friday whether authorities would pursue the death penalty, but said, ?everything is on the table.?

The 22-year-old is being held in a special housing unit at the Utah County Jail so staff can ?keep a close eye on him,? the Utah County Sheriff?s Office said in a statement.

Robinson is under enhanced supervision and will remain on special watch pending a mental health evaluation, a process that may take several days, according to Sgt. Ray Ormond.

Once Robinson?s mental health is assessed, Ormond says officials will determine which housing area is most appropriate for him.

The precautionary measures are standard for cases involving serious charges or potential behavioral concerns, Ormond said, noting that he has not been made aware of any specific suicidal comments by Robinson.

?He will continue to be monitored by mental, medical, and custody staff throughout the duration of his stay,? Ormond added.

Have authorities found a motive?

Authorities are working to understand what may have led Robinson to the rooftop where he allegedly gunned down Kirk this week.

Authorities are investigating whether Robinson?s romantic relationship with his roommate, who is transgender, could be connected to the shooting, Cox told CNN?s Dana Bash.

?This partner has been incredibly cooperative, had no idea that this was happening and is working with investigators right now,? Cox said.

The Utah LGBTQ+ Chamber of Commerce condemned the shooting in a statement Sunday.

?We are all grieving in this difficult moment,? said CEO and President Liz Pitts. ?And it will take all of us to change the narrative. By rejecting hate and choosing compassion, we can begin to build the bridges that will carry us forward.?

Investigators are also looking into the contents of a note Robinson left, Cox appeared to confirm to Bash on ?State of the Union,? but he indicated it was still under review.

?Those are things that are still being processed for accuracy and verification and will be included in charging documents,? Cox said.

Jud Hoffman, a vice president of the messaging platform Discord, said in a statement Friday there were ?communications between the suspect?s roommate and a friend after the shooting where the roommate was recounting the contents of a note the suspect had left elsewhere.?

Robinson, a third-year student in an electrical apprenticeship program who grew up in the small suburban community of Washington, Utah, was arrested following a 33-hour manhunt that drew national attention and fueled a wave of misinformation online.

While police investigate the killing, authorities have pointed to what they described as anti-fascist messages engraved on bullet casings in a rifle found near the shooting as potential evidence of a political motive.

One bullet was inscribed with ?Hey fascist! Catch!? ? a message Cox said Friday ?speaks for itself.?

Cox on Friday said Robinson was radicalized ?in a fairly short amount of time.?

A family member of Robinson?s told investigators the suspected shooter ?had become more political in recent years,? and had criticized Kirk at a recent family dinner, Cox said.

The messages on the bullet casings also included a mix of memes and allusions to video games. They featured a series of arrows representing the controls used to carry out an attack in the video game Helldivers 2 and lyrics of a popular Italian song linked to anti-fascists. Other engravings hinted more at connections to online trolling, including one that said, ?If you read this, you are gay LMAO.?

Robinson was ultimately arrested after his father recognized him in images released to the public and persuaded his son to confide in a youth pastor, a law enforcement source told CNN. A family friend then contacted the Washington County Sheriff?s Office, officials said.

Messages Robinson is believed to have sent on Discord were also among the clues that helped investigators zero in on him as a suspect, officials said.

The messages stated a need to retrieve a rifle from a pickup point, leaving the rifle in a bush, watching the area where a rifle was left and having wrapped the rifle in a towel, according to the affidavit. Investigators have said they discovered a bolt-action rifle wrapped in a towel near the scene of the shooting.

The Discord messages, which Robinson?s roommate showed investigators, also refer to engraving bullets and mention a scope and rifle being unique, officials said.

And in a Discord group chat following the shooting, Robinson joked his ?doppelganger? had carried out the crime, The New York Times reported.

After the FBI released surveillance images of a man in a stairwell at the Utah Valley University campus, an acquaintance in a group chat tagged Robinson?s username and asked, ?wya,? meaning ?where you at,? the Times reported.

Robinson replied within a minute, writing his ?doppelganger? was trying to ?get me in trouble,? the Times report said, noting the exchange took place around 1 p.m. Thursday, hours before Robinson?s arrest.

CNN has not independently confirmed messages in the Discord chat.

Following his arrest, Robinson initially spoke with some law enforcement but quickly went silent Friday morning after hiring a lawyer, sources familiar with the matter previously told CNN.

What will happen to Kirk?s podcast and tour?

?If you thought that my husband?s mission was powerful before, you have no idea,? Erika Kirk said in her first public address following her husband?s killing. ?You have no idea what you just have unleashed across this entire country.?

In an emotional tribute to her husband, Erika Kirk shared a series of photos and videos on social media of her holding and kissing her husband?s hands in his open casket. In one photo, she is seen sitting in a chair and leaning over the casket.

?You have no idea the fire that you have ignited within this wife,? she said in her address Friday. ?The cries of this widow will echo around the world like a battle cry.?

Charlie Kirk?s scheduled tour of university campuses, ?The American Comeback Tour,? will continue as planned, Erika Kirk said.

?There will be even more tours in the years to come,? she said, noting Americafest, Turning Point USA?s annual conference, will still be held in Phoenix in December.

?It will be greater than ever,? she said. ?The radio and podcast show that he was so proud of will go on.?

Erika Kirk said she has had to explain her husband?s absence to her two young children.

Thursday night, their 3-year-old daughter asked: ?Where?s Daddy??

?Baby, Daddy loves you so much,? she responded. ?Don?t you worry. He?s on a work trip with Jesus, so he can afford your blueberry budget.?

Friends, colleagues and fans also memorialized Kirk, saying he leaves behind a legacy of faith and love.

Andrew Kolvet, the executive producer of ?The Charlie Kirk Show,? said his friend and colleague died doing what he loved.

?Charlie was never afraid of intellectual combat. He was willing to go into any arena, debate with anybody and discuss anything ? and he loved it,? Kolvet told CNN?s Michael Smerconish on Saturday. ?It energized him, he knew that those interactions were what people were hungry for.?

Kolvet said Kirk was ?riveting? to watch and described the conservative political activist as spending ?all of his waking moments learning and studying and trying to hone his skills.?

Kolvet and others hosted a memorial edition of Kirk?s radio show and podcast Friday. Kirk?s promotion of challenging other people?s ideas through discussion and debate was at the heart of the podcast episode.

Kirk?s chair remained at the table, poignantly empty.

But seeing Kirk?s personal items, like his ties and toys left by his children, drove home the loss for Jack Posobiec, a conservative commentator who worked closely with Kirk.

In the days since his death, Kirk?s accounts across the internet have gained millions of followers, according to data compiled by CNN. Videos of Kirk?s political arguments promoting Trump and conservative priorities have also seen a surge in viewership, with many clips being traded back and forth by fans.

The words ?I AM CHARLIE KIRK? have become a rallying cry among Kirk fans on social media platforms since his death.

How are Kirk?s supporters responding?

Kirk?s supporters paid tribute to the activist at vigils in states including New York, Wisconsin, Virginia, North Dakota and Utah. Vigils and prayer circles honoring Kirk are also set to take place this weekend in several other states, including Florida and Colorado.

?We are Charlie,? said one mourner?s sign at a vigil Friday in Provo, Utah. ?And we won?t be quiet.?

?It was looking at that when it really hit me that he?s not coming back for those,? he said.

?Good men must die,? another sign read. ?But death can?t kill their names.?

Many of those at the vigils were young college students, a testament to his massive fanbase on college campuses. Turning Point USA, where Kirk was the executive director, has about 800 college chapters, according to the organization?s website.

One mourner, 22-year-old student Alexis Breuer, said Kirk ?came around at a point in time when a lot of us were afraid to voice our beliefs, were afraid of the backlash from our peers.?

?He was ? someone else that was in our age range that understood the generation that we were in,? she told Reuters at the Utah vigil. ?He was an example to us that we don?t have to be afraid. We can stand up for our beliefs eloquently and peacefully, without fear.?

Another vigil attendee, 24-year-old student Dallin Webecke, said the killing was ?very scary? but said supporters are clinging to one another for comfort.

?We are not alone and we are able to still keep fighting together,? he told Reuters.

At Utah Valley University, where 3,000 people had gathered to watch Kirk speak Wednesday when he was killed, many are still grappling with the shooting. Video of the incident shows students screaming and fleeing, and 911 calls reveal spectators? panic seeing Kirk be struck by the bullet.

Former Utah State Rep. Phil Lyman said Kirk continues to be a major global influence even after his death and witnessing the shooting would ?change the trajectory of? the students who were gathered at the campus for Kirk?s event.

?If Charlie?s wishes are fulfilled, then it will change it in a very positive way,? he told CNN?s Fredricka Whitfield.

Utah Valley University announced classes would resume Wednesday ? exactly one week after the attack. Mental health counseling will also be available for students, the university said.

It?s unclear whether Trump will attend the memorial celebrating Kirk?s ?remarkable life and enduring legacy? at the home stadium of the NFL?s Arizona Cardinals. Thursday, Trump said he has ?an obligation? to attend Kirk?s funeral. (CNN)

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