California man charged with murdering his 2 young children in Mexico, authorities say

A California man has been charged with the murder of his two young children in Mexico, authorities said.

Matthew Taylor Coleman, 40, of Santa Barbara, California, was charged Wednesday with foreign murder of United States nationals, according to the U.S. Attorney's Office for the Central District of California. He allegedly confessed to killing his 2-year-old son and 10-month-old daughter with a spearfishing gun, according to a criminal complaint. Mexican authorities had initially listed the children's ages as 1 and 3, respectively, in a prior update on the investigation.

Coleman had checked into a hotel near Tijuana, Mexico, with the two children on Saturday, Baja California prosecutor Hiram Sánchez Zamora's office said in a statement Tuesday.

On Monday at 2:54 a.m. local time, Coleman allegedly left the hotel with his children and returned at 6:33 a.m. that day without them, Mexican authorities said. He left the hotel about three hours later, according to Zamora's office, which shared security footage that allegedly showed Coleman checking into the hotel with the children and then leaving without them.

Mexican authorities responded to a 911 call around 7:30 a.m. Monday reporting the discovery of the children's bodies near a ranch about 18 miles from the hotel, Mexican authorities said.

The children were found in a ditch with "large puncture wounds" to their chests, according to the criminal complaint. Mexican authorities had previously said that the children were found with multiple stab wounds.

Coleman allegedly discarded the spearfishing gun and bloody clothes near a creek a couple of miles away, according to the criminal complaint.

FBI agents arrested Coleman in San Diego after he crossed the border via the San Ysidro bridge and he allegedly confessed to murdering his children, according to the criminal complaint. He had a cut on his hand from the spear, according to the complaint.

He allegedly told investigators that he "believed his children were going to grow into monsters, so he had to kill them," the complaint stated. He allegedly said he was "enlightened by QAnon and Illuminati conspiracy theories" and believed his wife passed "serpent DNA" on to his children, according to the complaint.

Coleman allegedly told investigators where he left the children's bodies, which matched the location where Mexican authorities found them, according to the complaint.

Santa Barbara police had received a missing persons report for a man and his two children who were "believed to have crossed the southern border into Mexico," the FBI said in a statement to ABC News Tuesday. "A joint investigation is underway among the Santa Barbara Police Department, the FBI in Los Angeles and San Diego, U.S. Customs and Border Protection and Mexican authorities."

The children's mother had reported the three missing after approximately 24 hours, according to the Santa Barbara Police Department.

"The mother was concerned for the wellbeing of her husband and their two children," the department said in a statement Tuesday.

She told police her husband did not tell her where they were going, and that she did not believe he would harm the children, according to the complaint.

U.S. authorities were able to track down Coleman's location in Rosarito, Mexico, on Sunday using the Find My iPhone app, according to the criminal complaint. They used the app again to find him at the U.S.-Mexico border Monday afternoon.

Coleman, who owns the Lovewater Surf School in Santa Barbara, made his first court appearance Wednesday in Los Angeles, during which a judge ordered he be jailed without bond. His arraignment has been scheduled for Aug. 31. Online court records did not list his attorney information.

ABC News' Anne Laurent, Jennifer Watts, Deirdre Littauer and Matthew Fuhrman contributed to this report.