GASTONIA, N.C.  — The six-day search for Maddox Ritch, the 6-year-old boy with autism who went missing at a North Carolina park, ended Thursday with the discovery of a body in a creek, officials said.

“I’m heartbroken,” Gastonia Police Chief Robert Helton told reporters during an emotional news conference. “Our community is heartbroken… This is not the end we had hoped for.”

Identification of the remains will be done by the medical examiner’s office, but authorities indicated they believe they are of Maddox.

Jason Kaplan, an FBI supervisory special agent, said investigators want to determine the cause of death and whether a crime was committed.

The body was found in a creek about one mile east of Rankin Lake Park, where Maddox was last seen with father and a friend on Saturday, Gastonia Fire Chief Phil Welch said.

It was partially submerged in about two to three feet of water. The area, thick with underbrush, had been searched numerous times.

Kaplan declined to comment on the condition of the body.

The FBI in Charlotte tweeted, “With heavy hearts we announce a body believed to be 6-year-old Maddox Ritch was found at approximately 1 p.m. off of Marietta Street/Old Dallas Highway in Gastonia. Maddox’s parents have been notified of the discovery. The investigation is ongoing.”

Hours before, the FBI tweeted that an “Underwater Search & Evidence Response Team is in the water at Rankin Lake Park” as part of the search.

On Saturday, Maddox took off running during a walk around the lake at a Gastonia park, a police spokeswoman said. Maddox’s father, Ian Ritch, said he and a friend were walking in the park when his son ran ahead, likely triggered by a passing jogger. Maddox was about 25 to 30 feet away when he broke into a sprint, Ritch said.

Ritch said he “was giving him just a little leeway, freedom” when he let him run up ahead, but he had a clear view of his son.

Maddox often would run ahead of him but would usually slow down and stop to give him time to catch up, Ritch said.

“I couldn’t catch up with him. I feel guilt for letting him get so far ahead of me before I started running after him,” Ritch told reporters on Wednesday.

911 call: ‘We searched everywhere’

Ian Ritch said he, the friend who was with them and park staff members first helped search for Maddox. Chief Helton said a part-time park employee reported Maddox missing.

According to a 911 call released by police, a caller told authorities Maddox’s parents had been searching for him for almost an hour.

“We searched everywhere,” the man said on the phone call.

Blue-eyed Maddox was last seen wearing an orange T-shirt with the words “I am the man,” along with black shorts and closed-toe sandals.

Federal, state and local authorities chased more than 150 leads, conducted hundreds of interviews, gathered surveillance videos from local stores and employed dogs, drones, sonar, ATVs and infrared technology in the search.

Ian Ritch, the father, spent some of Tuesday at the park with authorities retracing their steps, the FBI said.

What Maddox’s parents said

Maddox’s mother, Carrie Ritch, previously said her son has a contagious smile and laugh. He loved the park, bouncy balls and his teddy bear, she said.

“Maddox is my whole world and my reason for living. He’s mama’s boy.”

Maddox’s father said not being able to find his son has “been torture.”

“I’m not eating. I’m not sleeping. I’m just worried about getting my little boy back,” he said before Thursday’s announcement.

Authorities hoping to talk to jogger

Helton, the Gastonia police chief, said authorities want to talk to an unidentified male jogger who was in the park at the time and a professional photographer whom witnesses saw taking photos of other children dressed in Dr. Seuss costumes.

Hundreds of people were in the park on Saturday, including other blond-haired boys also wearing orange T-shirts, Helton said.

“But we need to know if you saw our blond-hair with the orange shirt,” Helton said.

How did Maddox’s autism affect the search?

Children with autism are often prone to wandering or bolting away. When children with autism go missing, rescuers get to know their likes and dislikes, and use familiar sounds, such as the voice of a cartoon character and a favorite song to draw them out during searches.

Maddox was described as nonverbal, which complicates the search for him. Hoping he would respond to his parents’ voices, authorities pumped prerecorded messages into Rankin Lake Park.

“Many of these children are more likely to respond to a favorite character, a unique interest or familiar voice,” said Lori McIlwain, a co-founder and board member of the National Autism Association.