Both men were aspiring law enforcement officers, studying criminal justice at Palomar College. Then their career paths diverged.
One was arrested earlier this month on suspicion of setting an Encinitas church and school on fire, and the other was lauded for working undercover to help catch him.
Tyler Carender, 20, is charged with causing more than a half-million dollars in damage to St. Andrew's Episcopal Church and Oak Crest Middle School in a series of early morning fires last fall.
The first fire, on Oct. 22, destroyed the youth center at the church. Investigators noted a set of Vans shoe prints at the scene, according to a search warrant for Carender's home, car and cellphone that was unsealed in San Diego federal court last week.
A week later, flames erupted in the middle school administration center, causing the ceiling to partially collapse.
And on Nov. 12, another fire broke out at the church's preschool building. Investigators suspected it was sparked by a Molotov cocktail thrown through a window. A neighbor reported seeing a man flee the scene.
Carender, who lives with his mother in a home that abuts the middle school, had been arrested in 2011 for firing an air rifle at middle school students from his backyard.
A few days after the third fire, a tipster called Crime Stoppers and named Carender as the arsonist. The person, who was not identified by authorities, then called a second time with more information.
According to the search warrant, Carender's Facebook page showed he had an interest in the fires. He posted below one news story with the comment: "I went to that middle school I really hope they catch the person."
Carender was pursuing a degree in administration of justice at Palomar College in San Marcos, and sheriff's detectives provided college police with a bulletin identifying him as a person of interest.
A fellow student working as a community service officer for the police department immediately recognized Carender as a classmate and agreed to help with the investigation, the court document says. The student, who was also not identified, fostered a friendship with Carender, and their early conversations revolved around their shared aspirations of going into law enforcement. But Carender expressed concern that he wouldn't pass the required background screenings, according to the document.
Carender also casually brought up the fires in their early talks, at one point saying that living in Encinitas was nice except for the recent crime wave there, the document said. He also asked his classmate if he had any training in investigating arsons.
During a hiking outing at Torrey Pines State Reserve in March, Carender again expressed concern about passing background tests, and the community service officer pressed Carender to tell him why. Carender said he had pleaded guilty to a DUI in 2015 and admitted to breaking into vehicles and a house and using drugs, according to the search warrant.
Carender added, "There's one more thing, man, but I can't tell you. I could go to jail for the rest of my life."
After some prompting from his new friend, Carender finally said, according to the search warrant, "Do you remember those arsons in Encinitas I told you about? … I did those."
Later, during the hike, the officer secretly activated a voice recorder on his cellphone and brought up the arsons again. Carender, who was wearing Vans sneakers, made more comments about the fires, the search warrant states.
Afterward, the officer reported the confession to his supervisor at the police department, wrote a report and submitted the recording.
Based on a federal indictment, agents with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives arrested Carender at his home on July 5. He pleaded not guilty and was granted release on $50,000 bond. His lawyer did not respond to a request for comment.