their case would rely heavily on the word of one man the killer himself, alexander bennett. this guy, bennett? >> absolutely. >> reporter: your case was gonna rise and fall on that? >> he was going to be the star witness against stephen cooke. >> reporter: bennett told jurors the same story he told investigators how he killed heidi. video cameras weren't permitted, but bennett's testimony was audiotaped. he decided to confess he says because of his faith and for heidi's family. >> i wanted to be a human being. i wanted to give a family some type of peace. i wanted to have faith enough and to grow up into a man and to accept and take responsibility for what i did. >> reporter: but the question still remained. if stephen cooke had planned heidi's murder, why had he done it? according to stephen, they were in love and planning to marry. but some of heidi's friends testified that she was so miserable in the relationship, she was preparing to leave. >> she had asked a friend of hers for a small loan for an easy storage facility in an effort to move out. >> reporter: and the real