On July 15, 2002, as she played with her best friend outside her family's Stanton, Calif., condo, 5-year-old Samantha Runnion was snatched, kicking and screaming, by a stranger who had said he was looking for a lost puppy. Twenty hours later her nude and brutalized body was found by a pair of hikers on a remote mountain trail 40 miles away, plunging her mother, Erin, and family, including Erin's longtime fiancé, Kenneth Donnelly, into the blackest grief. (Samantha's biological father had not been involved in her upbringing.) Finally last month Erin watched a Santa Ana, Calif., jury sentence Alejandro Avila, 30, to death for her daughter's kidnap, sexual assault and murder. Sitting in the front row, she sobbed quietly as the verdict was read. "She is missing so much—I cannot forgive him for that," says Runnion, 30, who married Donnelly, 36, in February 2003 and gave birth to their daughter Rose that August. "But I'd rather focus on what can come of this terrible tragedy."

Runnion says she found a renewed sense of purpose in the Joyful Child Foundation—which she and Donnelly, president of an Orange County investment firm, started in October '02 to promote child safety—and Samantha's Pride, local neighborhood watch programs (for more information, visit thejoyfulchild.org). She tells Maureen Harrington how she, her husband and her stepchildren Paige, 13, and Connor, 8, have coped with the pain of Samantha's death—and about the joy their new baby has brought.

We found out that I was pregnant in November 2002, just months after 'Mantha's death. It was a shock. The pregnancy forced me to make a leap. Suddenly my sanity became a priority. I had to focus on the baby. In the middle of my grief, I had to accept this blessing. Rosie is part of the healing for us, this incredible gift that came out of such darkness.

I also came to understand that I had to concentrate on my happy memories of Samantha. I think of her constantly, but I try to focus on who she was, not on how she died. The trial was hard for me because that was all about her death.

People didn't realize that I didn't know a lot of the details of her murder. I found them out in court and that was horrific. The opening arguments had me paralyzed. I learned for the first time that a woman heard screams at 8:30, during dusk. She wasn't far from where we think Samantha was at that time. It's been agonizing to think whether or not she lived through the night. I pray that she was only with him for three hours. That's easier to take.

Samantha's tears were found on the car door lock—he had a childproof lock on it. She could pull and pull on it all she wanted, but she could not get out. It's ironic that by crying and scratching him she identified her killer. I'm proud of her that by struggling—by leaving her tears and her fingernails with his DNA under them—she solved the crime. She was her own hero.

I haven't gone for counseling. I can get morbid, but I won't ignore the pain. I don't sleep a lot. When I put the kids to bed and Kenneth is asleep, I lie there thinking. I go to those bad places because I have to. I think about how I would hurt him if I could. But when I have those fantasies, I make myself sick. I've had to think through the "what ifs..." What if I hadn't been late leaving work? What if I could have saved her? You peel grief back layer after layer.

It was hard for Connor at first. He and Samantha were so close. He was just 10 months younger. I didn't realize until after she died that he didn't know how to button his shirt or tie his shoes; she had been doing those tasks for him. For a long time, Connor was terrified that the man would come and get us all. We took him to court one day so he could see that [Avila] was in chains and there were very big sheriffs on either side of him. He got comfort from that. We talk about what jail is and that he can't get out.

Paige, our 13-year-old, is a high-functioning autistic. It's as if Samantha's death forced her out of herself. It's like the switch for empathy was flipped. Now if she sees that someone is upset, she'll go to them to comfort them.

How do we cope? By working for other children and never giving up hope. When John Walsh's son Adam was taken, fewer than 60 percent of missing children in non-stranger abductions were saved. Now 98 percent are. That's awesome.

I will never stop missing Samantha, so I don't anticipate I'll ever stop trying to give her senseless murder purpose; the only purpose I can see is in raising awareness and motivating other families to make that extra little effort to stop these crimes from happening in the first place.

Kenneth has been my rock. Our new baby has brought joy and laughter back to our home. When Samantha died it was so hard to do fun things with the children; everything tasted more bitter than sweet. When I found myself pregnant, I felt I had to force myself to find a way to feel happiness again because I could not bring a child into a home devoid of joy.

With the trial over, we'll go back to having more fun with the kids. We go to the beach or to Disneyland. I'm excited about this summer. I think we'll get our lives back.