In this May 14, 2020, file photo, a person carries a sign supporting QAnon during a protest rally in Olympia, Washington. Credit: Ted S. Warren / AP

A Santa Barbara, California, father suspected of killing his two children in Mexico told the FBI he was a QAnon adherent and had to kill them because they had been infected with serpent DNA and he was saving the world from monsters, according to a criminal complaint filed in Los Angeles federal court Wednesday.

Matthew Taylor Coleman, 40, is charged with two counts of foreign murder of a United States national in the slaying of his 2-year-old son and 10-month-old daughter. He is accused of shooting them with a spearfishing gun on Monday in Rosarito — a beach community 30 minutes south of Tijuana, according to the U.S. attorney’s office.

Coleman runs the Lovewater Surf Co., a surfing school based in Santa Barbara, and is an alumnus of Point Loma Nazarene University in San Diego, according to the company’s website.

Coleman told FBI agents he killed his children by shooting a spear into their chests, explaining that he had been “enlightened by QAnon and Illuminati conspiracy theories” and “believed he was saving the world from monsters,” according to an affidavit in support of the complaint.

Coleman told federal agents he was “receiving visions and signs revealing that his wife … possessed serpent DNA and had passed it onto his children,” the affidavit states.

While QAnon encompasses a broad array of conspiracy theories, its followers generally believe that former President Donald Trump is fighting a deep-state of Satan-worshipping cannibals — including prominent Democrats and A-list celebrities — who are operating a child sex-trafficking ring.

It was not immediately clear whether Coleman had yet hired an attorney who could speak on his behalf.

Coleman’s wife contacted the Santa Barbara Police Department on Saturday to report that her husband had left the couple’s residence in a Mercedes Sprinter van with their two children, and she did not know where they had gone, according to the affidavit.

She told police that Coleman was not responding to text messages, but that she did not believe he would harm their children. She told police she was concerned because Coleman did not have a car seat for the children.

The next day, Coleman’s wife filed a missing persons report. Using the Find My Phone app, Coleman’s wife was able to determine that her husband’s phone had been in Rosarito on Sunday afternoon, the affidavit states.

Surveillance video obtained by Baja California investigators shows Coleman checked into a City Express hotel in Rosarito on Saturday with his two children.

Baja California prosecutor Hiram Sanchez Zamora said video shows Coleman left the City Express hotel on Monday morning at 2:54 a.m. with both children. A few hours later, he returned to the hotel at 6:33 a.m., but without his children, said Sanchez, who gave details at a news conference in Tijuana on Tuesday afternoon.

At 7:27 a.m. Monday, Baja California police received a 911 call about the shocking discovery of the bodies of two babies in diapers believed to have been repeatedly stabbed with a wooden stake. Their remains were discovered in a ditch by a farmworker near the El Descanso ranch, which is located at kilometer marker 55.4 on the scenic road between Tijuana and Ensenada.

Coleman’s son was found stabbed 17 times and his daughter stabbed 12 times. A “blood-stained wooden stake,” initially believed to be the murder weapon, was found near their bodies.

Witnesses of the discovery of the childrens’ bodies told Baja California media outlets they believed the killings were part of some type of satanic ritual or cult killing.

The same phone-locating service was used later Monday, showing that Coleman’s phone was near the San Ysidro Port of Entry at the U.S.-Mexico border, according to the affidavit.

The FBI asked law enforcement colleagues in San Diego to stop Coleman, who entered the United States in the Sprinter van without the children. Coleman was referred to secondary inspection and then taken into custody as he tried to cross from Tijuana into the U.S. at San Ysidro, according to the court affidavit and Baja California officials.

Customs and Border Protection officers reported seeing what appeared to be blood on the van’s registration paperwork, according to the affidavit.

When the children were not found with Coleman, FBI agents contacted law enforcement officials in Rosarito and learned that Mexican authorities that morning had recovered the bodies of two children matching the description of Coleman’s children.

Coleman later told FBI agents during an interrogation that he killed the children with a spearfishing gun, which he discarded a couple miles away along with some bloody clothes and a baby blanket, according to the affidavit. Mexican authorities were able to find those items and the murder weapon.

QAnon beliefs have been linked not only to political violence, including the Jan. 6 attack on the U.S. Capitol, but to violence grounded in delusions about the victimization of children. In 2019, an internal memo from the Phoenix office of the FBI called QAnon and adjacent conspiracy theories a domestic terror threat, citing at least two violent incidents.

The movement has had to pivot after Trump’s predicted day of judgment, known as “The Storm,” did not arrive as promised, and many people now believe that Trump is a “shadow” president.

A report by the FBI and Department of Homeland Security released in June warned of more violent action by adherents of QAnon, with some likely to begin believing that “they can no longer ‘trust the plan’ referenced in QAnon posts and that they have an obligation to change from serving as ‘digital soldiers’ towards engaging in real world violence.”

U.S. law allows the prosecution of murder committed in another country, so long as both the defendant and victim are U.S. citizens, and the defendant has since left the country where the crime was committed. The statute is rarely used and must be approved at the highest levels of the Justice Department.

The charge has been used twice in recent years in San Diego federal court to prosecute killings in Mexico. One case involved the 2011 murder of Yvonne Baldelli on an island off Panama. Her boyfriend returned to his home in the San Diego area and was later prosecuted. In the other case, Jake Merendino, a wealthy Texan, was murdered near Rosarito by his lover, who returned to his home in San Diego and was prosecuted.

Story by Wendy Fry, The San Diego Union-Tribune. Staff writer Kristina Davis contributed to this report.