It's one of most infamous missing-persons cases in Arizona history: A mother disappears, and as police and her family mount a massive search for her, cracks in their home life began to appear.

A housewife simply vanished into Tempe, Arizona's dry air on Sept. 1998. Where in the world is Cookie Jacobson?

It's a haunting mystery that cops desperately want to solve. Now Crime Watch Daily is looking for answers.

"We know that on that last day, when her husband arrived home, when her children arrived home, Cookie Jacobson was nowhere to be found," said Det. Allen Reed, Tempe Police Dept. (Ret.).

A week goes by with no sign of the 49-year-old homemaker. Hundreds of volunteers plaster missing-persons flyers all over town.

But during the search, detectives notice something strange about Cookie's son, Aaron: His absence.

"The reporters that spoke to me had said, you know, we find it unusual that Aaron doesn't want to really help in this search for his mother," said Det. Reed.

It puts Aaron on police radar, with looming questions. Why would the 16-year-old have anything to do with his mother's disappearance?

The Jacobsons adopted Aaron and daughter Laura when they were babies. By all accounts they led a normal, happy family life. But the facade would soon by shattered when cops get a call from a lady who overheard a conversation at a grocery store.

"She overheard that Aaron wanted to kill his mother, and that immediately got my attention," said Reed.

Cops ask the family to take a polygraph test.

"[Husband] Bill took the exam and passed with flying colors," said Reed. "Laura's test results were inconclusive. Aaron miserably failed the exam."

Soon detectives confront Aaron with the test results and press him for more information about his mother's disappearance.

"Aaron told me that he woke up that morning late for school," said Reed. "He walks into his mother's bedroom and he finds her dead in bed. He said that he then went to his sister and told her that he needed help in wrapping her body in a yellow sheet and getting rid of the body by putting it into a trashcan located in the alley. And he said that she complied."

Cops then question little sister Laura about her alleged involvement.

"I can tell you that she was only 13 years old," said Det. Reed. "She was confused, she was afraid, maybe she had been threatened."

From that moment on the investigation took a sharp turn, veering from a missing-person case to homicide.

"The probable cause that we had for the arrest was indeed a confession that they had found their mother dead in bed," said Reed. "That they confessed to getting rid of the body so they wouldn't be blamed for her death, which is exactly what did happen. We blamed them for the death."

But cops still don't have any idea how Cookie was killed. Then police records reveal what could be the seeds of Aaron's sinister plans.

One student reports Aaron telling him that "He wanted to kill his mother, and his sister wanted to do something to her too."

With search warrant in hand, detectives descend on the family home, where pieces of a deadly puzzle are found.

"Two trashcans were used in transporting her body to the alley," said Reed. "And we were able to find a substance, a bloody-type substance in the bottom of each of those trashcans. Later on, DNA analysis showed to us that was the blood of Cookie Jacobson."

What they don't find in the alley, or anywhere else near the home, is Cookie Jacobson.

And though police think they have a case against the children, it's not enough for the district attorney. Just a few hours after the arrests, Aaron and Laura are released.

Prosecutors say they need a body.

"The investigation showed us that her body had been taken to a landfill," said Det. Reed.

So more than 30 police and city workers sift through 8,000 tons of trash at the Butterfield Landfill several miles away in search of Cookie's remains.

"I regret to say we never found it," said Reed.

Cookie's brother traveled from California to see the horrific place where police say his sister was dumped.

"Once a year I drive by that landfill on my way to Yuma, and I look as I drive by I look out the car window and I know Cookie is there," said Reed. "Her body is there. That is her final resting place. It is not the place she'd want to be. I can tell you that. It is not."

Tragically, 18 years have now passed since that fateful day and there's another missing key piece of evidence making it impossible to bring the killer or killers to justice.

"When you go to a trial, you have to tell the jury a story, and the part of the story that I cannot tell is how Cookie's life was taken," said Det. Reed.

Cookie's kids are now adults in their 30s and have lived under a veil of suspicion all these years.

Crime Watch Daily went to Aaron's home, hoping he'd finally have some answers about his mother. No luck.

When approached, their father Bill also refused to talk to reporters.

The truth behind Cookie's disappearance remains a mystery. But cops say time is on their side and the truth has a way of seeping out.