No answer. The boy's grandmother, Kristina French, wasn't picking up either.
So Mott and his girlfriend paid for a ride from the airport, arriving at his house in Neptune Beach to find the front door open, the place ransacked and the gun safe emptied.
This initiated a frantic, days-long cross-country search for the ninth-grader and his grandmother. It began with concern for both of their lives, but then took some of the darkest turns imaginable.
"Kristina loves Logan dearly and Logan loves her just as much," the boy's mother, Carrie Campbell-Mott, wrote in a desperate Facebook post after the pair disappeared, according to Action News Jax.
She described French - who had become a grandmother to Logan in her late 30s and was now 53 - as one of the kindest, most caring people she had ever known. (French's employer, a school for autistic and disabled children, would later say much the same thing.)
Her son, Campbell-Mott wrote, was good and kind to his family. He had not made a sound when he was born and remained introspective through life - "always looking at the world, analyzing it."
Logan was also brave beyond his years about his diabetes, the mother wrote, which now concerned her gravely.
"If you have taken them we are begging you to return Logan and Kristina," she begged in her post. "Please. Without insulin he WILL die."
Wednesday passed with no sign of either. By the following night, a police cruiser stood guard in a light rain outside French's house, to which she had not returned, and from which guns had also been taken, First Coast News Reported.
A few miles away in Neptune Beach, police were still combing through the ransacked house where Logan had lived with his father.
A reporter saw investigators with buckets and sifters in the yard Thursday evening; the public would find out the next day what they were for.
Rumors began to circulate that something terrible had happened inside the Mott house some time between last Friday, when Logan was last seen at school, and Wednesday when his father returned.
At 5 p.m. Friday, high-ranking police and members of the Jacksonville Sheriff's Office gathered at Neptune City Hall to reveal what they knew.
Logan Mott was not in need of insulin, sheriff's office Director Ron Lendvay told reporters. The boy was believed to have taken a week's supply of medicine, and also stolen his grandmother's car and driven hundreds of miles north to Pennsylvania, where a surveillance camera had spotted him the previous day.
So Logan as still being sought. "We need to talk to him about what may have taken place in the house," Lendvay said.
And considering the missing guns, he was considered armed and dangerous.
Just as Campbell-Mott could not have imagined French hurting her son, she also could not believe that Logan would harm or intentionally kill his grandmother.
"It could have been an accident and he got scared and ran. We have no idea," she wrote on Facebook after the news conference, as reported by Action News Jax. "He is likely scared, alone and deeply confused."
"Logan Mott if you are reading this I love you," she wrote. "I'm here. I love you. Please call me. I will help you. Mom."
That night, less than an hour before midnight, the sheriff's office announced that Logan had been found.
He had not called his mother and come home, but had instead traveled all the way from Neptune Beach to near Buffalo, where federal agents detained him at the Canadian border.
A judge had already issued an arrest warrant for auto theft by then, though Logan was still described as only a person of interest in his grandmother's death.
The sheriff's office did return a request for further details on Saturday morning.
In a statement released to ABC News and other outlets after Logan's capture, his mother remained as optimistic as might be thought possible.
"We are relieved he is safe and in custody and we just ask for everyone to give us time to sort out what happened," she wrote. "That no matter what, Logan is our child and we love him and are standing by him to help in any way."
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)