Jessica had been on her way to the bowling alley's game room, and was last seen at the front door waiting for an uncle who was bringing some baseball cards, according to West Virginia State Police.
Her disappearance launched a massive search that included more than 50 FBI agents, local police, family members and volunteers.
Authorities used helicopters and bloodhounds in the search that continued throughout Friday night and Saturday.
Authorities studied a security tape from the bowling alley, but turned up nothing helpful, Mosquera said.
The video camera takes pictures of the pool room, the main parking lot and a side parking lot.
Agents went to the bowling alley several times Saturday to interview staff and people who might have been there Thursday night.
"It was a league night and we know everybody,'' said assistant manager Darlene Forsyth. "A stranger would stand out.''
Flyers with pictures of Jessica holding a teddy bear were plastered on the front door of the bowling alley and other place of business in Berkeley County on Saturday.
Into the early hours of Saturday, the Martinsburg barracks remained a beehive of activity, with troopers and detectives going in and out.
Other troopers stood by in the parking lot of Pikeside Bowl while search dogs combed the area behind the popular bowling alley and billiard hall.
All day Saturday, police searched on the ground, interviewing neighbors along U.S. 11 near Pikeside Bowl and flying overhead in helicopters.
Jessica, a second-grade student at Berkeley Heights Elementary School, was 4 feet tall, 60 pounds, with blonde hair that flowed midway down her back. She was wearing a red and pink flowered one-piece dress when she disappeared Thursday.
The father of an 8-year-old himself, Mosquera said he kept seeing his daughter's face as the search for Jessica continued.
"It's gut-wrenching, it's just so tragic to see," said Mosquera. "You've got a lot of dedicated people here. This little girl could have been anybody's little girl."
About six FBI agents, notebooks in hand, were at the bowling alley late Saturday interviewing bowlers. At one point, agents appeared to confer with each other and then left the bowling alley.
Kimberly VanMetre, 34, of Martinsburg, said she bowled regularly with Jessica's parents.
She said news that a body had been found was announced at the bowling alley.
"I was hoping that wasn't true," she said.
"She's a very sweet girl," she said of Jessica. "I don't understand why anyone would do what they did."
VanMetre said Jessica recently had invited some of her friends to the house to show them her new school clothes.
"She was just a kid you'd always want," she said.