(CNN)On May 11, 2011, Amy Fry-Pitzen checked her 6-year-old son out of Greenman Elementary School citing a family emergency.
Four years after mother's suicide, search for son continues
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Three days later, Fry-Pitzen's body was found in a hotel room in Rockford, Illinois. She had committed suicide.
A note was found saying that her son, Timmothy, was safe with people who would love and care for him.
"You'll never find him," Fry-Pitzen's note read.
Four years later, at 10 years old, Timmothy is still missing.
Where is Timmothy? Did Fry-Pitzen pass him off to someone willing to raise him? Or did she kill her young son and dispose of the body before taking her own life?
"I have one image. It's the day I dropped him off at school and he's off -- running off to class -- and that's pretty much the last image I have in my mind of him," Timmothy's father, Jim Pitzen, told CNN's "The Hunt with John Walsh."
Jim had met Amy at a party, and the two started dating long-distance for a year or so. Early on in their relationship, Amy revealed she struggled with depression. Jim was confident she could learn to better deal with her issues in the embrace of a healthy relationship since Amy first showed symptoms of depression after the divorce with her first husband.
In 2003, Jim received a call from a hospital in Cedar Rapids, Iowa.
"She had taken some pills, I guess, and [had been] sitting on the edge of the cliff, and supposedly passed out and fell off the cliff," Jim said.
The following year, Amy became pregnant -- and the couple's life seemed to turn around dramatically. They married, and on October 18, 2004, Amy delivered a healthy baby boy.
"She just adored that little boy, and he just adored her," Amy's mother, Alana Anderson, told "The Hunt."
Amy added the extra "m" in his name because she wanted it "a little different from Timothy," according to her mother.
Soon after, Jim and Amy started having problems in their marriage again: they quarreled about money and about Amy's traveling alone with friends. Amy's depression flared up, and she threatened divorce. Amy's biggest fear, according to her family and friends, was that a judge would take her son away because of her mental health issues.
"I know that this woman was so disturbed, and in such serious need of some type of help. Somebody that loved her needed to intercede, and it didn't happen," host John Walsh said.
The day before Amy took her own life, she made several brief cell phone calls from an unknown location to family members, including one to her mother. Amy assured her mother that she and Timothy were safe. Timmothy also spoke to a family member, and didn't seem to be in any distress.
When they found Amy's body the next day, finding Timmothy became the priority.
Working from receipts found in Amy's hotel room, police reconstructed the mother and son's final odyssey: a fun-filled, three-day road trip with stops at zoos and water parks.
In all the security video footage from their stops, mother and son seem relaxed and cheerful.
Lead investigator Lee Catavu of the Aurora, Illinois, Police Department told "The Hunt with John Walsh" that the last known area Amy and Timmothy had been in was predominantly farmland.
"Any one of those locations could, in theory, be a spot where she could have done a hand-off of her child to someone," he said.
It wasn't until the evening of Friday, May 13, that Amy was caught on a camera without Timmothy at a grocery store in Winnebago, Illinois. From there, she checked into the Rockford Inn, where her body was found the next day with the door locked from the inside.
"One would think that if someone, let's say, were told a story to take Timmothy, that they would then ultimately see that he, in fact, does have a family out there who still misses him and loves him and wants him to return," Catavu said. "For them not to reach out ant try to reunite them, I mean, it's hard to figure out."
Timmothy Pitzen is an outgoing, inquisitive child. He loves playing in and around water. He may be tall and mature looking for his age.
If you've seen Timmothy Pitzen or have any information as to his whereabouts please make the call. 1-866-THE-HUNT or go online to CNN.com/TheHunt. We'll pass your tip on to the proper authorities and if requested will not reveal your name.
See more of Pitzen's case on "The Hunt with John Walsh," at 9 p.m. ET/PT Sunday, August 30.