Sky Metalwala has not been seen since his mother reported leaving him alone in an unlocked car on a city street after running out of gas on Nov. 6, 2011.
The woman, Julia Biryukova, refused to be formally interviewed by detectives, and police determined that her car started normally and wasn't out of gas.
Her estranged husband said the boy's disappearance bore a strange resemblance to an episode of her favorite television show, "Law & Order: Special Victims Unit."
In a news release Monday, Bellevue Police Maj. Pat Spak said the department has pursued more than 2,200 tips and leads in the case, and investigators remain frustrated that they've been unable to find the boy.
In May, three Ohio women were found alive more than a decade after they disappeared. That news sparked new hope for Solomon Metalwala, Sky's father.
"They haven't found his body, so that means he's out there somewhere," Solomon said in May.
Solomon said he's holding out hope that he'll see his child again.
"It means there's hope for me. There's hope for everything," he said.