DAVISON TWP, MI -- Police are refocusing their efforts in the search for the 9-year-old autistic boy who went missing Saturday, July 4, from Lake Callis Recreation Complex.

Police do not believe the boy is in the lake, as it was searched a combined six times by two dive teams -- one from the Genesee County Sheriff's Office and another from the Lapeer County Sheriff's Office, said Lt. Jay Rendon with the Davison Township Police Department.

Each dive team also used sonar to scan the bottom of the lake and searched all bodies of water within a two-mile radius of the complex.

Nothing was found.

Video surveillance from the pavilion at Lake Callis Recreation Area, which is located off North Gale Road between Davison Road and Court Street, shows Omarion "Mars" Humphrey walking from the pavilion toward the nearby splash pad at 5:09 p.m. Saturday, July 4.

He went out of view from the cameras, and hasn't been seen since.

The park complex remained closed Monday, July 6, as specialized search-and-rescue teams continued combing the park and surrounding area. There has been no sign of the boy.

"The thing with kids is that they are mobile. He may not have been in a particular spot when we searched there yesterday, but that doesn't mean he's not there now," Rendon said.

Omarion is severely autistic and does not speak but will come if called, police said.

He is described as 4 feet tall and 70 pounds and last seen wearing no shirt, no shoes and black shorts with a red stripe.

Volunteers and search and rescue crews have looked everywhere within a two-mile radius of the complex since he went missing, Rendon said.

"The question now isn't so much where have we searched, it's where haven't we searched," Rendon said.

One of the volunteers out Sunday at the lake was 26-year-old Richfield Township resident Allen Babcock.

"I chose to volunteer because with me being part of a scanner page that keeps the community informed and helps the community. That I should volunteer my time to go and help search for Mars," he said, having searched near Chatwell Club Apartments at Gale and Lapeer roads, from the Davison Dog Park to the Davison Township Police Department and from the airport on Gale Road to the east.

In the hours after Mars went missing, a Michigan State Police helicopter hummed overhead. Police K-9 and private K-9 search and rescue teams tried to track him, but with the thousands of people -- and scents -- at the park over the weekend, a track was unsuccessful.

Even teams from the Michigan Department of Corrections -- who usually use physical evidence and clues to track escaped convicts -- were looking for the child.

"They actually track people -- normally bad guys -- but they know what to look for," Rendon said, pointing down to the ground. "They are highly specialized in tracking."

An Amber Alert was issued Sunday morning, July 5, and the complex remained closed to the public as the search continued.

About 600 volunteers arrived at the complex Sunday to help. Police asked area residents to check sheds and outbuildings in their yards, but there were no reports of the missing boy.

Police sent volunteers home as night fell Sunday while specialized crews continued searching overnight.

They thoroughly searched the railroad tracks north of the park that run east and west, Rendon said.

Still nothing.

"We are not leaving any stones unturned. We are exhausting every resource we have," Rendon said.

On Sunday, the boy's mother, Khisha Humphrey, drove from Pontiac to help in the search as well. She thanked volunteers and described her son as a boy who loves music, computers and video games. Humphrey said Omarion was at the lake with his foster family.

Humphrey said the search has been taxing, saying, "Every hour is like 10 hours."

She said her son has, in the past, hidden in the backyard or in a cabinet at home, and Sunday, she said she thought he may have hidden in someone's playhouse when he disappeared.

"I'm just so scared to leave here, because what if he comes back," she said.

Monday morning, K-9 units, several police agencies and volunteers were on the ground searching again. Although the K-9s cannot track the boy, they will be able to pick up his scent if he is hiding somewhere he cannot be seen.

Deputies from the Lapeer County Sheriff's Department were to grid-search a bean field nearby.

Anyone with information on Omarion's whereabouts has been asked to call 810-732-9911 or 911.