Fenerman (in the movie played by Michael Imperioli of Sopranos fame) is the detective in charge of Susie's case and a recent widower. He's part of the novel's love triangle; he has an affair with Susie's mom.
He lets Susie's killer get away. Yet, early in the novel, Susie says, "I still thank God for a small detective named Len Fenerman" (1.45). Why is she such a fan? For one thing, she feels sorry for him. But, that's not enough to account for it. OK, the quickest way to get on Susie's good list is to think about her, remember her, and care about her. She's even mad at Harvey for not remembering her. But Fenerman does. She is a part of his life, and he'll never forget her. That's why she has a soft spot for him in her ghostly heart.
I felt sorry for him. He had tried to solve my murder and he had failed. He had tried to love my mother and he had failed. (16: Snapshots.50)
Fenerman is not the brilliant detective who solves the crime. Nor is he the bumbling detective who makes tons of mistakes, but nonetheless manages to solve the crime. No, Fenerman is a very human figure and is marked by failure, from the suicide death of his wife (which he, not we, might consider his fault), to his failure to suspect Mr. Harvey, to his failure to win Abigail's love.
He fails to solve Susie's crime for the very reason he's what we might call a 'good' cop. He doesn't want to treat Mr. Harvey unfairly, doesn't want to violate his civil liberties. He acts in such a way as to preserve the rights of ordinary citizens from unlawful search. OK, this is a tad thin – Fenerman could have done a better job. He could have taken Harvey in for questioning, found an excuse to search the house, etc. Fact is he simply didn't figure Harvey for the killer, and he was distracted.
First, Lindsey does what he was too reluctant to do – break into Harvey's place and find the evidence. If he hadn't been making love to Susie's mom in the underbelly of the mall, he would have gotten Jack's call, and arrived in time to arrest Harvey. But, knowing Fenerman, he might even have botched that. In spite of his failure, we like him, just like Susie does, because he's a decent guy, trying to protect those who can't protect themselves.
OK, it isn't very nice having an affair with the married mother of the murdered girl you are investigating. But, according to Susie, this was something necessary for her mother. Susie says that for her mother making love with Fenerman is "a doorway out of her ruined heart" (15.66). In any case, Abigail basically uses him. He doesn't seem to mind, but wishes it could have turned into something more.
As with so many of the characters, Susie sees Fenerman's frequent post-Abigail sexual liaisons in his room over the barbershop as part of his process of understanding life, of dealing with the ugly world he's faced with in his work. As we seen throughout the novel, this consensual sex as a move toward understanding is presented as a sharp contrast to Harvey's violent sexual mode. Susie understands this about Len Fenerman and sees herself as acting similarly. She says,
I had come to both pity and respect Len in the years since my mother left. He followed the physical to try to understand things that were impossible to comprehend. In that, I could see, he was like me. (20.8)
For Susie, following the physical refers to her ghostly followings of the living, but also to her making love to Ray, using Ruth's body, a couple of chapters later. Susie needs that consensual sexual encounter to, in a sense, get back what Harvey tried to take from her. Likewise, Fenerman probably needs to remind himself that sex can be beautiful and good.