A Michigan man who believes he might be D'Wan Sims -- a 4-year-old boy who went missing in 1994 and was believed dead -- has submitted his DNA to the police for testing.

The unnamed man walked into the Livonia Police Department on Dec. 11., where he submitted a DNA sample exactly 25 years after Sims's mother, Dwanna Harris, told police she was shopping with the child at the Wonderland Mall in Livonia when he mysteriously vanished. The surveillance video inside showed Harris inside the mall, but there weren't any images of Sims.

Harris said she's been in communication with the man -- but has doubts he might actually be her son. She told the Detroit Free Press that she asked him about personal information only she would know, like his birthmarks and date of birth, but she said he was unable to answer the questions.

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“I have no clue, whatsoever,” she said at her home on Friday. “You would like to be hopeful.”

Police Captain Ron Taig said investigators couldn't find anything to make them confident about Sims actually being at the mall.

“I was here at the department and we looked at all of the video, we checked everything, and we never saw D’Wan [Sims] with Ms. Sims,” Taig told WDIV-TV.

Police said they first heard of the man's theory after he posted the belief of his identity on Facebook and shared the second thoughts he was having over what his parents told him about his childhood.

“I guess what’s odd is that he claimed that he didn’t want any of this information out in the media and from what I understand he has put this out on social media,” Taig said.

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But Harris said she is wary and has been the target of “constant ridiculing” due to the circumstances of Sims's disappearance.

“With every other thing that has happened ... it’s been negative about me,” she said.

In April, Brian Michael Rini claimed he was 14 and told police in Kentucky that he was Timmothy Pitzen, an Aurora, Illinois, boy who disappeared in 2011 at age 6. Authorities said Rini told them he escaped captors who sexually abused him.

Federal authorities said they were suspicious after Rini refused to be fingerprinted. DNA testing quickly revealed his true identity. Rini had been released from a state prison in March after serving more than a year on burglary and vandalism charges. Prison records show he was accused of making up stories during his time there.

When confronted with the DNA results, Rini said he had watched a story about Timmothy on ABC's "20/20" and wanted to get away from his own family, the FBI said. Authorities said he twice earlier portrayed himself in Ohio as a juvenile victim of sex trafficking.

He faces trial next year on charges of aggravated identity theft and lying to FBI agents.

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Sims would now be 29 years old. Anyone with information on his case is urged to contact Livonia Police Department’s missing persons unit at 734-421-2900.

The Associated Press contributed to the report