I agree that compassion for the suspect could indeed interfere with the investigators' judgment, but I also think that compassion for the victim and the victim's family can be a good thing, giving them a boost to their motivation and determination to solve the crime and giving the rather abstract concept of justice a concrete reality. And I think it is probably something that can't be helped. From what I know, the FBI tends to deal with some very grisly and/or large scale crimes (especially the Investigative Support Unit, which aids local officials investigating cases involving serial murder and rape). Not only are they less likely to sympathize with the suspect such cases, but feeling at least some degree emotion for the victim and victim's family is, I think, unavoidable, and I find that to be a good thing simply because I'd worry about someone who could look upon or hear about a grisly crime (and some of these crimes are beyond terrible) and not feel at least some emotion. These are the best law enforcement officials in the country, and I think they are well-trained and experienced enough not to let their emotions interfere with their judgment. I remember reading in a book by former FBI agent John Douglas, who worked in the ISU, that he and his colleagues often did get quite an emotional reaction to their cases, and that many of them, himself included, had at least one case that haunted them (the book by the way, is called Journey into Darkness, and is pretty good if you are interested in this sort of thing). I also remember him mentioning that FBI agents who work in the missing and exploited children's unit are especially motivated by emotion for their victims; the walls of the unit are covered with their pictures, which are, I think, marked in some way when the child is recovered, and it seems like they will stop at nothing to get every single one of those pictures marked. I don't have any factual basis for this of course, but somehow I just don't think they would be as motivated and determined as they are if there were nothing on the line but a paycheck and an abstract (as opposed to concrete) idea of justice.