Jacksonville police said a body found buried behind Mott's home on Seagate Lane is thought to be French, but police said Friday they were waiting for medical examiners to confirm the identity.
"The burial site was excavated today and human remains were located". He said they had evidence of foul play and "potential criminal violence" inside the home.
At this point, JSO says 15-year-old Logan Mott is still missing, as is the silver Dodge Dart.
It is the same home where police have been investigating the disappearance of teen Logan Mott and French, his grandmother.
A surveillance camera at a gas station in south-central Pennsylvania picked up an image of Logan and the auto on Thanksgiving at 1:15 p.m. Ron Lendvay, a director of investigations and homeland security for the Jacksonville Sheriffs Office, told Florida Times Union.
Officials say Mott is "considered armed and dangerous" and is likely driving the vehicle the pair was last seen in - a 2015 silver Dodge Dart with Florida tag DLL T42.
Logan Mott was not in need of insulin, sheriff's office Director Ron Lendvay told reporters. "We want to find out what happened to Kristina and we need time for that to happen", according to a statement from Mott's mother.More news: Trump Jokes He Won't Undo Obama Turkey Pardon
Logan and his grandmother, Kristine French, were slated to pick the teen's father up from Jacksonville International Airport on Wednesday but never arrived. Call 911 if you see him.
"No matter what, Logan is our child and we love him and are standing by him to help in any way", she said.
"Logan has so many friends and family that are desperate to hear from him", she said.
Police say the boy's father, Eric Mott, returned from vacation on Wednesday to find his son and his mother missing, and his Neptune Beach house ransacked. "So it's just baffling", Carrie Campbell-Mott said.
She the station that the last time she spoke to her son was Sunday night, and everything seemed fine.
Told the mother, 'There just wasn't any indication that there was anything wrong, nothing.
He was detained by border patrol agents in Buffalo, New York while he tried to cross over in Canada.