Betrayal turned deadly: The killing of celebrity hair stylist Fabio Sementilli

When famed stylist and hair care executive Fabio Sementilli' was found him stabbed to death on the patio of his home in Woodland Hills, California, on January 23, 2017, the crime was assumed to be a burglary gone wrong. Since 2012, police were noticing a rising trend of burglaries in upscale neighborhoods in Los Angeles that were causing alarm among residents.

As detectives got to work and looked deeper, they began to realize something more sinister than a burglary gone wrong happened at the home, something that would lead them on what they described as a trail of love and murder.

"However this went down," Fabio Sementilli's sister Mirella Sementilli told ABC News, "it was executed brilliantly because we were deceived."

A monthslong investigation by the Los Angeles Police Department would result in Sementilli's wife Monica and her lover Robert Baker arrested and charged with first-degree murder. Documents obtained by "20/20" provide a chilling firsthand account of how Baker said he plotted and carried out Sementilli's murder.

"The ultimate goal of the killing was so that he and Monica could be together," according to Baker's account.

A new "20/20" airing Friday, May 17, at 9 p.m. ET and streaming the next day on Hulu, examines the investigation that revealed what authorities said was a deeply plotted murder coverup, the surprising discovery about who investigators allege would want Fabio Sementilli dead and details recently uncovered in new court documents obtained by ABC News.

Fabio Sementilli was a larger-than-life father of three who had made a major name for himself in the hair industry. Family and friends said the 49-year-old was beloved by all.

"He used to tell stories and he would engage people for hours," Mirella Sementilli said in a new "20/20" interview. "He'd always make everything really funny."

A buoyant hair stylist in Canada, Fabio Sementilli worked his way to the top of high-stakes hair competitions across the globe, the pride of his Italian immigrant family. He moved to Southern California in 2007, living with his second wife Monica Sementilli and their two teen daughters.

Friends who visited Fabio and Monica Sementilli's home described the welcoming atmosphere, full of friends and family gathering for food and drinks.

Documents obtained by "20/20" provide a chilling firsthand account of how Robert Baker said he plotted and carried out Fabio Sementilli's murder.

Elyse Bleuel, a friend of Monica's who often visited the Sementilli home, recalled how Monica Sementilli relayed that "everything's really great" in her almost 20-year marriage to Fabio Sementilli.

"Monica was my fancy friend," Bleuel said. "Everything she touched was elegant. Her home was elegant."

When Monica Sementilli urgently texted Elyse in January 2017, asking her to come over, she rushed to the house. Bleuel recalled the unusual way she was a greeted when she got to the house: A stranger escorted her inside with a warning: "Don't step in the blood."

Inside, police discovered what they described as an extremely gruesome and bloody scene. Fabio Sementilli was stabbed multiple times in his neck, face and chest. His prized red Porsche, which was later found 5 miles away with droplets of blood on the inside, was missing.

"I'm sitting with Monica," Bleuel remembered about that visit. "She could not put words together. She was like, 'I'm not a wife anymore,' over and over. That was her mantra, like she was processing this."

Family described the disbelief they felt after learning about the hair industry executive's murder.

"It felt like a nightmare," Fabio Sementilli's son from his first marriage, Luigi Sementilli, said in an interview with "20/20." "After a while, it just feels surreal...When you go through this kind of tragedy, it just doesn't feel real."

As family and friends mourned Fabio Sementilli's passing, police were on the lookout for possible suspects. They were tipped off about a mystery man who showed up unexpectedly at a memorial gathering at the family home. "It seemed out of place because this was more of a memorial for Fabio. This was more of Fabio's people," Bleuel recalled.

One friend at the memorial found the man's presence so unnerving that they took a photo of him and turned it over to police. Detectives learned that this mystery man was Robert Baker - a popular racquetball coach in the Los Angeles area.

"Rob always had a smile. And he's a good-looking man...He presents this super charismatic personality and he always seems happy," says Alana Evans, who knew Baker from his previous career in the adult film industry.

However, Evans discovered a darker side of Baker years later. He was a registered sex offender after a conviction for lewd and lascivious acts with a minor in the early 1990s.

Baker also shared a surprising connection with Fabio Sementilli's inner circle: he was Monica's racquetball coach. Investigators studied that photo from the memorial more closely and saw what appeared to be an adhesive bandage on Baker's finger. Baker's DNA was already in the law enforcement database from his prior conviction. Detectives compared it to blood droplets found in Fabio Sementilli's Porsche which they had recovered early in the investigation -- and it was a match.

With investigators now believing they had enough evidence to put Baker at the scene of Fabio Sementilli's murder, they set up surveillance and obtained search warrants for his communications. As the Sementilli family continued to mourn for days, weeks and months - investigators finally moved in on a car Baker was driving on June 14, 2017. They put Baker under arrest for the murder of Fabio Sementilli - but he was not the only one in handcuffs.

"Detective Parshal called us... and he said, 'OK -- we've made an arrest for your brother's murder. We arrested Monica Sementilli and Robert Baker,'" Mirella Sementilli recalled. "I blacked out."

Investigators claimed Fabio's wife Monica didn't actually commit Fabio's murder - but they allege that she did have a role in planning it. According to the indictment, Monica Sementilli and Robert Baker had been having an ongoing affair and conspired to kill Fabio so the couple could be together and collect life insurance money. This was unfathomable news to the tight-knit Sementilli family.

"I don't know what to think in that moment. I'm, like-'Are you sure this is right?'...This all seems so, so far-fetched," Luigi Sementilli told ABC News. "And then, of course, I learn about the quote/unquote "real investigation" and everything else that was going on that was held private from everyone - up until that point."

The felony complaint against Monica Sementilli and Robert Baker details what investigators depict as an elaborate scheme for the two lovers to get away with murder. Prosecutors say with Monica at the helm, she and Robert Baker orchestrated a plan to murder her husband Fabio. They allege critical to the plot was Monica ensuring Fabio would be home alone the day of the murder.

Court documents state Monica drove to a nearby Target to establish her alibi, aware that her daughters would be out of the house at the time of the murder. While at the Target, court documents state that Baker and another unknown assailant entered the Sementilli home, stabbed Fabio multiple times, and staged a burglary - fleeing the scene in the victim's Porche and leaving behind blood evidence from Baker's cut finger.

Investigators discovered Monica had given Robert access to the Sementilli family's home security system and prosecutors allege she had been monitoring the security camera feed on her phone while Baker entered the Sementilli house, to let Baker know when the victim would be home alone. Prosecutors also allege Monica intentionally planned for her youngest daughter, Isabella, to arrive home first and find her father's body.

"When all of it came out...my brain just shattered with the dichotomy of the mother and the wife and the home and the life that they created," Bleuel said.

Robert Baker and Monica Sementilli were charged with first-degree murder and conspiracy to commit murder. The two pleaded not guilty to all charges.

"The affair has been known, that's a given," Monica's defense lawyer Leonard Levine told "20/20."

"But it doesn't mean she had anything to do with the murder of her husband, and she denies it totally and has since the very beginning."

As the pair awaited trial, Robert Baker decided last July to plead "no contest" to all charges relating to the murder of Fabio Sementilli, including admitting to the special circumstance allegations of murder for financial gain and murder while lying in wait. Pleading no contest means Baker did not contest the charges and accepts the facts alleged by prosecutors without admitting to being guilty. He was sentenced to life in prison without the possibility of parole.

"It sounded like I was listening to the Devil speak," said Mirella Sementilli when asked what it was like to hear Baker's voice in the courtroom. She and other family members gave victim's rights statements at the hearing.

After his sentencing, Baker said he planned to testify at Monica Sementilli's upcoming trial. Court documents obtained by "20/20" revealed that in February 2024 Baker gave a detailed account of what he claimed was his role in the murder to Monica Sementilli's defense team.

In the documents, Baker alleged "Monica had nothing to do with the planning or execution of the murder." He said he acted alone after she told him, "divorce was not an option, her family does not do divorces." Baker described the murder in chilling detail, saying he "slipped into the house with a hunting knife...looking to kill Fabio so he and Monica could be together." He said he rushed Fabio, stabbing him "anywhere there was open skin."

"He says he's going to get up in front of the jury and tell the truth," Monica Sementilli's defense attorney Leonard Levine told "20/20." "If he testifies and testifies truthfully, then we're hopeful his testimony will be believed by the jury."

As of May 2024, 10 months after Baker's sentencing - Monica Sementilli remains in jail, denied bail. Her trial has been delayed by one legal proceeding after another but is currently scheduled to begin December 2024.

As Monica Sementilli's fate hangs in the balance, those close with Fabio tell ABC News they feel they are moving toward some semblance of closure. Monica's daughters, however, are continuing to support their mother leading up to her trial.

At Robert Baker's sentencing, Monica's daughter Gessica proclaimed that she and her sister "want to clearly state that we'll continue to stand by our mother as we have done for the last six years and we'll fight for her innocence."