A 15-year-old Florida teen is in custody at the U.S.-Canada border, hours after police discovered the body of a woman believed to be his missing grandmother in a shallow grave near the boy's home, the Jacksonville Sheriff's Office reported.

Logan Tyler Mott was detained by the U.S. Customs and Border Protection as he tried to enter Canada from Buffalo, New York, sheriff’s deputies said.

The Jacksonville Sheriff's Office had called Mott “armed and dangerous” and a person of interest in the death of his grandmother, 53-year-old Kristina June French.

Mott was being watched by French at her Neptune Beach home while his father, a Jacksonville Sheriff’s Office corrections officer, was on vacation.

Mott’s mother, Carrie Campbell-Mott, said the boy’s father, Eric Mott, was on vacation with his girlfriend. Eric Mott took an Uber home from the airport Wednesday after French never showed up to get them, Campbell-Mott said.

When they got home, the door to their home was open and the house was ransacked, Campbell-Mott said.

Eric Mott's guns were missing from a gun safe, Campbell-Mott said. French’s home in the Mayport area also was ransacked. Her weapons were gone, along with her Dodge Dart.

Mott and French were reported missing after Logan didn't show up to high school on Monday or Tuesday. French also didn't show up for work Monday or Tuesday. A warrant was issued for his arrest Thursday on a charge of auto theft, deputies said.

Originally, deputies believed that Tyler Mott and French may have been traveling together in the Dodge Dart. A missing child alert was issued by the Florida Department of Law Enforcement.

The teen and the missing vehicle were spotted Thursday on surveillance video in south central Pennsylvania, the Jacksonville Sheriff’s Office reported.

In a statement, Campbell-Mott she was “relieved” that her son was in custody.

“We just ask for everyone to give us time to sort out what happened,” Campbell-Mott said. “That no matter what, Logan is our child and we love him and are standing by him to help in any way. We want to find out what happened to Kristina and we need time for that to happen.”

Campbell-Mott said a sheriff’s detective will fly to meet Logan on Saturday.

In a statement, the May Institute, a nonprofit organization that employed French, said it was “truly devastated” to learn of her death.

“Kristina was a friend and a role model to so many people. … She was a true champion for people with disabilities and advocated tirelessly for human rights.

“We have lost a beautiful person and she will be dearly missed. It is a very sad day.”