When relatives of Myrtle Jean Simmons-Brown and Sergio Brown were unable to get ahold of either mother or son on Sept. 15, they called the cops.

The next day at around 2 p.m., Myrtle's body was found by a creek near the home she shared with Sergio in the Chicago suburb of Maywood, according to police, who said at the time that they were unable to locate her son. Cause of death was determined to be multiple injuries due to assault, the Cook County Medical Examiner confirmed to E! News, and her case was ruled a homicide.

"It's a sad but hopeful time, and we will all get through this together," Myrtle's artist son Nick Brown wrote in a Sept. 17 Instagram post. "Mom always told me, 'tough times don't last' and our last conversation about tough times being temporary is my beacon of hope."

The painter thanked his 73-year-old mother for being "strong, caring, diligent, fancy, funny," and for supporting his craft. He added, "My brother Sergio is still missing. If anyone knows where he is I want him to know that I love you and please come home."

Several weeks later, Sergio was arrested on a warrant for first-degree murder in connection with their mother's death.

The 35-year-old was taken into custody Oct. 10 in San Diego, Calif., where he's currently awaiting extradition to Illinois to face murder charges, according to the Maywood Police Department. Public records show his next court date is Nov. 13.

E! News has reached out to Maywood Police and the Cook County State's Attorney's Office for comments on the pending case but has yet to hear back.

But events of the past month suggest a shocking spiral for the NFL journeyman, who was once known for his celebratory backflips after Notre Dame victories during his college football days.

At the time, he credited his mother for his skills.

"Me and my brother were always just goofing around in the house," Brown explained to student paper The Observer in 2009. "It really started after the movie 3 Ninjas came out. We just started trying to flip and stuff outside with mattresses. My mom started getting scared, so she said if we're going to do all this flipping, we might as well learn how to do it so we won't hurt ourselves. I've just been flipping since."

Sergio has yet to be formally charged and E! News has so far been unable to find out if he has an attorney. But this is what we know about the situation leading up to his arrest:

Who is Sergio Brown?

Sergio was born May 22, 1988, in Maywood to Myrtle and Mario Brown, a onetime college basketball star at Texas A&M. 

In past interviews, Sergio provided childhood highlights like being faster than all the other neighborhood kids and performing with a neighborhood tumbling group. But his family, which included brother Nick, suffered a blow when Mario died of lung cancer in 2002. Sergio was 14 and just starting at Proviso East High School, where he played football and competed in track and field.

Sergio was a four-star safety recruit out of high school and chose to attend Notre Dame, eventually starting for the Irish as a junior while earning his degree in business marketing.

"He's a guy you can't help but root for," teammate Steve Filer told The Observer of Sergio in 2009. "He's a great guy. You can't help but just cheer for him and hope he does his best."

Sergio went undrafted in 2010 but was signed by the New England Patriots, the first of four teams he played for over the course of seven years.

After two seasons in Foxborough, Mass. (the second including a trip to the Super Bowl), he joined the Indianapolis Colts. In his third season there, he got his first start for the team on Oct. 5, 2014, 12 years to the day after his dad's death—which he said his mom pointed out to him before the game.

"Once my mom reminded me, it just felt like it was right," Sergio told the Indianapolis Star. "Honestly, the more I thought about it, the more it gave me peace of mind. It made me feel like everything was going to be OK. It let me go out there and be free."

After an on-field performance that Star sportswriter Zak Keefer described as one of the finest days of Sergio's career, Myrtle reportedly told her son, "Your dad would have been proud of you."

That would be Sergio's last season with the Colts, however, after which he played a season apiece for the Jacksonville Jaguars and Buffalo Bills.

On May 5, 2016, a video posted to NFL on Fox's Facebook page showed the 6-foot-2 athlete in cap and gown at a graduation ceremony, the caption reporting he'd received his MBA from the University of Miami.

"Mama! We made it, Mama!" Sergio said into the camera for Fox Sports' PROcast as he walked into an auditorium. Laughing with some fellow graduates, he added, "We're not just dumb jocks."

He played his final eight NFL games for the Bills, who signed him that November, and after his exit from the league he went to work for Google.

"I'm one of those people that says life is what you make it," Sergio said in February 2018 on the podcast Innovating Life With Jon Sabes. "What are you really doing with your free time? I decided, you know, let me get a little bit of money, let me figure out what I'm going to do with this money, and go to school, and invest in myself."

After his contract with the Bills was up, he recalled, "I was...doing a lot of networking, and just trying to figure out what's next on the off-season. I got my degree, so I wanted to really start a business or something. Through the networking and me figuring things out around this time last year, I was talking to the director of healthcare from Google, and he offered me a job."

At first it was a no. "I cannot do this with Google," he recalled thinking. "I don't know what's going on, but I was like, 'You know what, yeah, I'm going to do it.' I took that leap of faith, and I'm here now."

According to his LinkedIn profile, Sergio spent about seven months as a health account manager at Google, followed by short stints as a product manager for FameBit and director of business development for marketing agency DAC in Chicago until June 2019. Most recently he's listed as founder/CEO since 2013 of Tastemakers LLC, a "creative agency that specializes in integrated marketing, space activation, and online digital ad sells."

What happened after Sergio Brown's mother was killed? 

Maywood Police said they considered Sergio a missing person after his mom was found dead Sept. 16 by a nature walk next to Silver Creek, which cut behind her house. 

On Sept. 18, a 51-second video posted to an unverified Instagram account showed a man who appeared to be Sergio calling reports of Myrtle's death "fake news, fake news, fake news." The man in the video alleged, per NBC 5 Chicago, "It has to be the FBI that came into my house" and said agents paid him an "unwarranted" visit on "Bob Marley's death day." (The anniversary of Marley's death is May 11.)

The reported account in question has since been taken down. Police told the Chicago Sun-Times Sept. 19 that they were aware of the video and were "looking into its authenticity." Detectives still considered Sergio missing, they added.

On Oct. 3, TMZ reported a witness allegedly seeing Sergio partying in Tulum, Mexico, and published a two-minute cell phone video of what appeared to be the former football player in red swim trunks dancing with a big group of people in broad daylight at an outdoor bar.

Meanwhile, Sergio's brother was anxiously awaiting progress in his mother's case.

"It's really sad, at this stage, that the Cook County State's Attorney's Office is not upholding public safety or justice for my mom, Myrtle Jean Simmons-Brown," Nick posted to Instagram Oct. 8. "My mom is gone, my dad is gone, and my brother is missing. It's not about saving face its about saving justice."

When was Sergio Brown arrested in connection with his mother's death?

Officers from the San Diego Police Threat Management Unit along with unspecified other local and federal agencies arrested Sergio on a fugitive warrant for first-degree murder as he crossed back into the U.S. from Mexico on Oct. 10, according to the Maywood Police Department.

Further details of the investigation have not yet been made public. Brown waived extradition during an Oct. 11 court appearance and, per public records, as of Oct. 19 he's being held without bail in San Diego Central Jail.

"Our family is thankful that the Cook County State's Attorney's Office answered our call for urgent and immediate action in the case of our beloved Myrtle Jean Simmons-Brown," the Simmons-Brown family said in a statement. "We are also heartened by the news that Sergio Brown has been apprehended and returned to the United States unharmed. Our family is prayerful that, as the investigation progresses, more answers will become available, shedding light on the circumstances surrounding this heartbreaking incident."