Del Mar true crime writer Aleida Wahn takes readers into the courtroom

A Del Mar true crime writer’s latest work, “Deadly Obsession and a Fiancé Murdered”, explores the 2021 murder of beloved Cathedral Catholic High School teacher and coach Mario Fierro and the trial that followed three years later.

A history teacher and track and football coach at Cathedral, Fierro was described as loyal, genuine, hilarious, strong in his faith, and committed to his students. He was 37 years old when he was shot and killed in front of his San Diego home by Jesse Milton Alvarez, the ex-boyfriend of his fiancée and fellow Cathedral Catholic teacher Amy Gembara.

“My book is a deep analysis of the case and trial for those who could not attend the trial. I take the reader into the courtroom as I attended all of the pretrial hearings and every minute of the trial,” said author Aleida Wahn. “This case devastated the San Diego community, and ever since I started writing about the case, people have contacted me wanting to know what truly happened.”

Wahn believes the case offers a good look at the criminal justice system. Gembara was being stalked by Alvarez and went to the court for help just 13 months before the fatal shooting. Wahn’s book analyzes why her restraining order request was denied and whether a restraining order would have prevented Alvarez from legally purchasing a firearm.

“The book examines whether there could have been intervention before it was too late, addressing signs that were missed,” Wahn said. “It is my hope that by examining these critical issues, future tragedies can be prevented.”

The ebook is available to download on Amazon.

Wahn, a former attorney, has been a true crime writer for the last 12 years.

“I try to find cases that I feel are really compelling and that really touch us, it’s not just about making it sensational,” Wahn said. “For me, it is really about looking into the trial and examining cases and the legal issues and what lessons we can learn to do better in law or society.”

“Deadly Obsession” is Wahn’s fifth book and she is now segueing into developing a true crime show for a streaming service. Already, she has appeared as an expert on Court TV, a “48 Hours” episode about the search for Maya Millete, and recently appeared in the “TokTok Star Murders” documentary on Peacock about the 2021 murder of Ana Abulaban in downtown San Diego.

For Wahn, Fierro’s murder hit close to home. Cathedral Catholic is almost in her backyard and her circle of friends includes the parent of one of Mario’s former students as well as another whose daughter was supposed to sing at Mario and Amy’s wedding: “She was going to sing at the wedding but instead sang at the funeral mass,” Wahn said.

When Wahn heard the details of the case, that Fierro was an innocent victim after his fiancée had been stalked by an ex and denied a restraining order, her attorney’s brain kicked in: “What can we learn from this case?”

For all the cases she has written about, she spends time in the courtroom to experience and get the information firsthand, and offer her own analysis. With Fierro’s case, it was an extremely emotional trial.

“The facts of this case are truly horrifying,” Wahn said. “You should be able to break up with somebody and go on with your life.”

Four months after Gembara broke up with Alvarez in December 2019, she filed a domestic violence restraining order. “He couldn’t take the fact that the relationship has ended,” Wahn said. Alvarez had continued to try to contact her multiple times, threatened suicide, tried to break into her apartment twice, followed her to Disneyland California Adventure, cyberstalked her and forced her to move.

Alvarez filed a 13-page response attacking each of her claims and making many ugly points against her and the judge found both parties credible and the evidence to be a tie in favor of Alvarez. The judge found that Gembara had not met her burden of proof that abuse had occurred within the Domestic Violence Protection Act.

“It was 13 months after the restraining order was denied that Mario was murdered,” Wahn said.

While Alvarez swore under oath he would not contact Amy again, his stalking behavior continued. He tried to ingratiate himself into the Cathedral Catholic community, attempting to befriend employees and even applied for a job as a food service worker through a private company. Alvarez worked in the cafeteria at Cathedral Catholic in October 2020 but was discovered and escorted off campus.

“He’s literally gone off the deep end in this obsession to be close to Amy,” Wahn said. “And then it all falls apart when Amy gets engaged to Mario.”

The couple got engaged on Sunset Cliffs and Cathedral Catholic announced the engagement of two of its teachers on Facebook on Dec. 19, 2020. Alvarez, who was in Peru with his family at the time, saw the post and began to spiral. Within 12 hours he found out where Fierro lived and 16 hours later did a Google search on how to hire a hitman. A week after the engagement post, he made multiple online searches on “how to get away with shooting someone” and “how to kill your ex’s fiancé”—a trail of digital evidence that would later be submitted in court to show premeditation.

Alvarez had purchased two firearms on Dec. 9, 2020 and the defense argued this was before he knew about Fierro. When he returned to San Diego on Jan. 14, Alvarez took shooting lessons and asked the instructor about the best place to shoot someone. On three occasions in January, he was on the Cathedral campus, pretending to be a student, even appearing in a school news broadcast segment.

In the days leading up to the murder, he went to Fierro’s North Park home and found out what kind of car he drove. On the morning of Feb. 1, he waited for about an hour for Mario to leave for work, firing seven shots and striking him six times.

Alvarez was arrested that night after his history with Amy was unraveled and witnesses reported seeing his car at Mario’s home. There was also an audio-video of the shooting recorded by a neighbor that was submitted anonymously to CrimeStoppers. The prosecutor played the haunting sounds during his opening statement.

The two-week trial began on Feb. 26, 2024 and Wahn’s book goes into all of the details of the legal proceedings, including Alvarez’s appearance on the witness stand: “He did not help himself at all.”

Wahn’s book also includes the victims’ impact statements read after the Feb. 5, 2025 sentencing when Alvarez received life without the possibility of parole.

One of the most moving statements came from Amy, who had since moved out of state and read it on video. She spoke about how kind and loving Fierro was and about finding light in darkness, standing up for women who experience domestic violence from a partner who can’t take no for an answer.

“I think that was so powerful that she was able to say ‘I don’t want to be a victim anymore, I want to be a survivor, ’” Wahn said.

To purchase the ebook, visit Amazon.com Learn more about Wahn at aleidalaw.com