'I Made a Terrible Mistake'

The water was cold, the mystery deep. It was the summer of 1999 when scuba diver Carl Claren decided to go for a swim in a suburban Cleveland quarry near the new house he was building. As he dove along the shallow edge of the quarry, he noticed something unusual.

"There was a duffel bag, and I figured there was something in there, brought it up in the yard, unzipped it and the leg and the foot fell out," Claren told "20/20."

Inside the canvas duffel, he found rocks -- and a dead baby boy with a stab wound and a head injury, his umbilical cord tied off with a barrette.

A Town in Shock, a Girl in Denial

The body of the nearly full-term baby shook the small Ohio community of Columbia Station so deeply they gave it a real funeral, a grave and a headstone bearing the name: Baby Boy Hope. Community members vowed not to rest until they knew who among them could do such a thing.

Lorraine County Sheriff's Detective Karl Yost became consumed by the mystery, developing a picture of the killer in his mind.

"I think we all wanted to think there was some kind of monster behind this, because who else would do this besides a monster?" Yost said.

But while he looked for the monster, just a few miles away was someone totally different, a 10th-grade girl, Jessica Coleman.

Jessica was a pretty, popular student-athlete with good grades -- and a terrible secret. When Jessica was a freshman, she and her boyfriend, Tom Truelson, fell in love and became sexually active.

The following fall, just as Tom was preparing for college and the two teenage lovers were worried about parting, she started to feel her body changing. She missed periods. But being just 15 and athletic, irregular cycles were not that unusual. By the fifth month, she began to worry.

She and Tom bought a pregnancy test and the results were positive. She was pregnant with his child. Jessica panicked. "I wanted it to be wrong. I thought, how can I tell my family and what are people going to think of me?" she said.

They made a decision to simply ignore the results. Perhaps, they thought, if they didn't acknowledge the situation, "it might just go away," she said.

Of course, it didn't. Still, she did her best to make sure her pregnancy went unnoticed by her family and friends. "My body actually did not change at all. I didn't gain any weight, because I had an eating disorder at the time. I wouldn't eat. I was afraid to eat, I was afraid to show, I was afraid that people would find out," she said.

Psychiatrist Gail Saltz, author of "The Anatomy of a Secret Life," said denying the pregnancy was a defensive device for Jessica.

"When somebody gets pregnant, you think of them as being 'a woman.' But in fact, this is really still a child. ... Something like this would be, of course, totally traumatic. When a person is traumatized basically beyond their capacity, you might delude yourself into believing quite easily that 'I can somehow wish this away,'" Saltz explained.

But Jessica was doing more than wishing. She and her boyfriend did desperate, dangerous things to hide their secret.

"A lot of times, Tom would stand on my stomach. ... I don't know why, I'm so ashamed that we ever did that, or that I ever allowed that to happen, that he denies ever happened," she said.

But hiding and ignoring and denying and even the torture of someone standing on her stomach did not stop the steady growth inside Jessica.

Five days after a basketball game in which she scored seven points, Jessica gave birth. "I was at school and I felt like I was sick, and I called my mom and I got dropped off at home. I didn't feel good, and I went to the bathroom and that's when it happened," she recalled.

'I Was So Scared'

But her newborn didn't appear to be healthy to her. "There was no crying. There was no movement or anything, and I was so scared. I was in shock the entire time. I cut the cord, obviously, but I have no recollection of doing so," she said.

She and her newborn were both in bad shape. Jessica was bleeding, and while walking from the bathroom into her bedroom, she fainted.

"I passed out holding him. So I wake up and I'm laying on the floor in my room and I have no idea what I'm going to do," she said.

Her mother called her to dinner. Jessica laid the baby on the floor inside her closet and joined her family for dinner at the table; but she couldn't eat. In the meantime, inside her closet, the newborn was slowly dying.

"He just looked like he was suffering and there was something really wrong. And what I ended up doing is terrible. I just felt like I was taking away his pain," she said.

In her anguish, Jessica said, she stabbed the baby. According to the coroner's office, that wound was not the lethal injury.

The coroner noted that "a blunt impact to the head, and possible brain injury, was the cause of death of this infant." Law enforcement personnel believe these injuries are consistent with Jessica's statement that she blacked out and fell on top of her baby.

Jessica's secret baby, whom she had privately named Stephen, never made it out of her bedroom alive. She called her boyfriend, Tom, but he could not make it from college until the next night.

When he finally showed up, Jessica said, he told her he would take care of the body, which is how her baby landed in the flooded quarry a few miles from her home.

"We were never going to tell anyone. It had gone so terribly wrong that by this point in time coming forward wasn't even an option any more," she said.

For six-and-a-half years, that pact stood. Baby Stephen's short life was a secret. Meanwhile, the police searched for the story behind Baby Boy Hope.

Yost was committed to solving the case. "I kept saying I'm going to solve this case if it's the last thing I do. I'd stake out the grave site from time to time, on dates of interest, the date of the burial, the date we found the baby," he said, hoping that perhaps the child's mother or father would visit the grave.

Still, the secret held. But across town, Jessica said her life was crumbling. Tom went off to college and they broke up. She said she could not recover from the deep secret she held. Jessica said she began drinking too much, had a DUI and used cocaine.

"Over the last few years, I started having like, mini nervous breakdowns, I guess you would call it. Just anything would trigger it," she said.

No Longer Able to Hide Her Secret

Five years after her baby's death, one bright light did enter Jessica's life. His name is Matt McKenzie, a local barber and her new boyfriend.

McKenzie began to talk with Jessica about marriage. But as a proposal was in the air, Jessica could no longer keep the secret from the man she hoped to spend her life with. She told McKenzie about her secret baby, Stephen.

She told me I had to know. "She started crying, sobbing, and she leaned on me and wanted to talk to me. It was very emotional because she was so upset about it," he recalled.

But the couple's friends overheard her confession -- and before long, Yost began to get anonymous phone calls about the death of the newborn he knew as Baby Boy Hope. After six years, Yost finally had a name to go with the picture of evil in his mind -- Jessica Coleman.

"She walked up to me when I got to the house and she was already sobbing and apologizing and asking me not to consider her an evil person or a monster," Yost recalled.

When Yost, who wanted to see the case of Baby Boy Hope's death in black and white, heard Jessica's story of pain and isolation, he saw lots of gray.

"I was expecting to meet one type of person, when in fact, I met somebody else. I know that 15-year-olds can make mistakes and I certainly categorize Jessica Coleman as a 15-year-old girl confronted with a situation where she saw absolutely no hope, no way out and did one of the most desperate acts anyone can do. Was it a mistake? Absolutely. Does she deserve to be punished for it? Yes, she does," he told "20/20."

Armed with confessions from Jessica and her ex-boyfriend, Yost took them to court. Truelson pleaded guilty to obstruction and gross abuse of a corpse.

Although she was 15 at the time of the crime, Jessica was tried as an adult -- and pleaded guilty to charges that included child endangerment and involuntary manslaughter.

After calling it one of the hardest decisions he had ever had to make, the judge sentenced her to six years in state prison.

Now 23, Jessica started her prison term just last week. She plans on finishing her college degree while in prison, and hopes to someday share her story with other pregnant teens, warning them about the destructive power of harboring such dark secrets.

"You have to tell somebody, you can't carry it with you. Your entire future could be based on what your decisions are for the next few months," she said.

Jessica said she agreed to give "20/20" this exclusive interview to reach out to other pregnant girls who may be facing crises similar to the one she faced. She said she hopes it may encourage them to turn to programs like Safe Haven, which didn't exist when she was pregnant but is now in place in 46 states.

She knows that some people may never forgive her for the death of her secret child.

"I made a terrible mistake, and nothing will ever change what happened then. But maybe I can prevent this from happening to somebody else. And maybe, by seeing me on today, there could be even one girl that is sitting there dealing with the same things I was dealing with and maybe tonight will tell her parents."