Amari Harley was playing in a Jacksonville park with relatives Sunday before his lifeless body was found in an underground water holding tank

The body of a 3-year-old boy was found inside an underground water tank in a Florida park Sunday night hours after he went missing — and police have not ruled out foul play, PEOPLE confirms.

On Sunday afternoon, Amari Harley and his family had gathered for a party in Bruce Park in Jacksonville, Assistant Chief Scott Dingee of the Jacksonville Sheriff’s Office told reporters at a news conference Sunday night.

Amari was last seen playing with relatives in the park, said Dingee. At about 3:30 p.m., his family realized he was missing and began searching for him.

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After searching unsuccessfully for the child, his family called 911 at about 4:45 p.m. to report him missing, said Dingee.

More than fifty officers, detectives, and members of the air and canine units searched for the boy.

Officers called the city’s public works department to check the underground water holding tanks in the park. After draining one of the tanks, officials found the boy’s lifeless body.

“Frankly, we do not know how he got into this water holding tank,” said Dingee. “The opening was large enough for someone to fit inside, so they were concerned he may have gone in there.”

Credit: Jacksonville Police Department

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Dingee said foul play has not been ruled out. An autopsy was completed, the medical examiner’s office tells PEOPLE, but officials have not yet released the results.

“This case is obviously active and ongoing. At this time all options are on the table,” Dingee said.

Police are asking anyone with information to call the Jacksonville Sheriff’s Office at 904-630-0500.