By Holly Yan, CNN

A caretaker reports a child missing and gives a detailed account of what happened. But as the story unravels, the caretaker becomes the suspect.

That's what happened when the father of 5-year-old AJ Freund said the boy vanished -- then later confessed he had actually stashed AJ's lifeless body in the basement.

That's what happened when the mother of 7-week-old Shaylie Madden claimed she and her infant were both abducted -- a story authorities now call a hoax.

And that's what's happening now in the case of 4-year-old Maleah Davis, who was reported missing May 4 and still hasn't been found.

Her mother's ex-fiance was taking care of Maleah and said he and the girl were kidnapped by a trio of mysterious men near Houston.

But police are finding more holes in Derion Vence's story -- as well as blood in his home and signs of decomposition in his car.

A life marred by a brain injury and alleged abuse

In just her first four years, Maleah had already endured multiple brain surgeries and had been removed by child protective services.

The surgeries were needed to treat an injury -- the cause of which remains uncertain.

Her mother, Brittany Bowens, said she took Maleah to West Houston Medical Center last July because she was lethargic, but nurses didn't examine her head.

Weeks later, on July 28, Maleah fell while she was sitting at the table eating by herself, Bowens said.

The girl suffered a deep gash on her head, and once again her mother rushed her to the hospital. Doctors discharged Maleah without performing a CT scan, Bowens said.

Five days later, Maleah suffered a seizure, Bowens said. Maleah was then taken to a children's hospital.

"They did a CT scan, and that's when they told me there was bleeding on the left-hand side of her brain," she told CNN. "At that point, it was a life or death situation."

A few days after doctors operated on Maleah, child protective services arrived at her home.

"They didn't find anything because we're not those kinds of people," Bowens said.

But that same month, child welfare workers placed Maleah and her two brothers with relatives after allegations of abuse. A judge later allowed the siblings to return home in February.

Three months later, Maleah vanished and is still nowhere to be found.

From caretaker to alleged victim to suspect

Derion Vence, the ex-fiance of Maleah's mother, was taking care of Maleah on May 3. What happened after that depends on who you believe.

Vence, 26, initially told police he was driving with Maleah to pick up her mother from the airport when he heard what sounded like his tire popping.

When he stopped to investigate, a blue pickup truck pulled up and two Hispanic males got out, Vence said.

He said one of the men commented, "Maleah looks very nice, looks very sweet." The other man hit Vence in the head, and he lost consciousness, Vence said.

Over the next 24 hours, Vence said, he drifted in and out of consciousness in the back of the kidnappers' pickup truck. He said at one point he noticed a third abductor in the truck.

When he woke up the evening of May 4, Vence said, he was abandoned on Highway 6 -- but Maleah was not there. He said he walked to a hospital for help.

Houston police say they've uncovered a litany of evidence contradicting Vence's story.

Surveillance footage at Vence's apartment complex showed him leaving the afternoon of May 3 carrying something heavy in a large black trash bag, according to a probable cause affidavit.

Vence later comes back to the apartment and leaves "with cleaning supplies including bleach," the affidavit states.

Meleah has not been seen since.

Police also found blood in the hallway and bathroom of Vence's apartment. DNA from the blood matches DNA from Maleah's toothbrush.

And surveillance footage at the hospital that Vence said he walked to showed he was actually dropped off in a silver Nissan Altima. It was the same car Vence was driving to the airport -- and that Vence said he hadn't seen since the night before.

When canine officers sniffed the car for evidence, they responded to "the scent of decomposition in the vehicle," the affidavit states.

Vence was arrested Saturday on suspicion of tampering with evidence -- a human corpse, police said.

Tampering with a human corpse is a second-degree felony in Texas. If convicted, Vence faces between two to 20 years in prison.

But authorities have not said whether Maleah is dead or alive, or where she might be.

CNN reached out to Vence several times last week but did not hear back. It' not clear if he has an attorney, as his scheduled court appearance Monday was postponed.

A boy's father reported him missing, then showed police his grave

The disappearance of 5-year-old Andrew "AJ" Freund last month prompted a widespread search across northern Illinois.

But he wasn't really missing. His father later confessed that he hid the boy's body in a basement and then buried AJ in an empty lot.

It was a stark contrast to the father's original story. Andrew Freund Sr. called 911 the morning of April 18, saying he couldn't find his son.

In reality, police said AJ likely died three days earlier after being punished for soiling his clothes.

Authorities also found a video on the cell phone of the boy's mother, JoAnn Cunningham, showing AJ badly beaten, according to now-sealed court documents obtained by the Northwest Herald.

"AJ is seen to (be) naked except for some small bandages around both wrists and circling his hips," one document states. "AJ is seen to be holding an ice pack to his face and when he removes it he is seen to have deep red bruising around his eyes."

The video marked a turning point in the investigation. When police showed it to Freund on April 24, he told them his wife caused AJ's injuries and described what he said happened the night AJ died.

"He believed AJ died on Monday morning after spending a prolonged time in a cold shower," the documents state. "Drew explained he wanted Joann to stop with the hard physical beatings and do some less violent form of punishment. Drew said cold showers was decided (as the alternative)."

After the confession, Freund took police to a shallow grave in Woodstock, where they found AJ's body covered with straw. An autopsy revealed he died of blunt-force injuries.

Both parents have been charged with murder.

Investigators say a mom threw her infant down a ravine

North Carolina police scrambled to find Krista Madden and her 7-week-old daughter last Thursday after someone called 911 and said the two may have been kidnapped.

Madden, 35, was later found walking on a country road. She told authorities she managed to escape two captors wearing ski masks, but that the kidnappers still had her infant daughter, Shaylie.

While Henderson County sheriff's deputies searched for Shaylie, someone called 911 to report the baby was found at the bottom of 75-foot ravine, along with a car seat.

Investigators now believe Madden threw the car seat down the ravine, Henderson County Sheriff Lowell Griffin said.

When the car seat hit the ground, Shaylie apparently rolled out. The baby was not seriously injured.

Her mother now faces an attempted murder charge.

"She did provide enough information about her involvement that gave us probable cause," the sheriff said.

A mother waits in agony

While we now know the fates of AJ and Shaylie, Maleah's whereabouts remain a mystery.

Soon after Maleah's disappearance, her mother said it was easier to believe Vence's story that a trio of kidnappers took her child.

"It gives me hope to know that she may be alive if someone else took her," Bowens said.

But as time passed, she started doubting her ex-fiance's story.

"The way he's going about things is suspicious," Bowens said. "I've been out here doing what I need to do as a mother. I've been trying, and he hasn't been by my side not one time."

Now Maleah's mother has no choice but to worry, wonder and wait.