A 21-year-old Florida mother was taking care of her two sons when she suddenly vanished from their home in 2008. Denise Amber Lee's story ended in tragedy, but her quick-thinking proved vital in helping police catch the man who killed her.

That Jan. 17, Denise's husband, Nathan Lee, returned to their North Port home after work around 3:30 p.m. to find their children Noah and Adam, who were 2 years old and six months old at the time, alone and placed in the same crib.

Unable to locate Denise, Nathan dialed 911 to report her missing. The call went to the Sarasota County 911 call center, triggering a massive search.

A new "20/20" episode, "Life on the Line" airing Friday, Oct. 10, at 9 p.m. ET on ABC and streaming the next day on Hulu.

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