Mystery, romantic suspense, and urban fantasy novels often start with a dead body, and the main character’s goal is to find out the who, what, when, where, and why of his death so she can solve the crime.
The first hook for the reader is curiosity about the victim and the crime as well as the main detective/character’s personality, etc.
Most readers will allow the writer time to set up the situation and to gather the first clues, but a certain point, the reader’s patience and interest will wear thin unless the writer gives the reader a reason to care about the victim. Simply getting justice for the victim isn’t enough to keep most readers reading the whole novel.
The simplest way to make the reader care is to make the victim someone the reader would care about instantly -- a child, an innocent, a good person, or a person with a job that matters like being a school teacher, doctor, social worker, or an honest cop.
Even someone who was a jerk or bad person will matter if he died doing something decent, or he had survivors who care. A weeping mother or wife who begs for justice is a strong motivator for the detective and the reader because they create an emotional stake in the person’s death. If the detective must prove it was murder, not suicide, so the young widow with little kids will get death benefits, the solution will matter.
If nothing about the victim will give the detective or the reader any reason to care that he was murdered, then the detective must have another reason to solve the crime. Perhaps, he will lose his job because his failure rate at solving crimes is so high, or he’s caught in a political situation where only solving this crime will save his career. The victim could be one of a string of serial killings, but the killer has made several sloppy mistakes in this killing which could be his downfall so the detective is trying to stop other murders as well as solving this one.
A method used in TV shows like CSI or BONES is to make the good guys and their scientific methods as important as the crime’s solution. We care about them more than the rotting corpse of the abusive pimp at the crime scene, and their lives are the soap opera that drives the emotional plot while the science drives the mystery plot.
Having the killer go after the detective or people he cares about is also a tried and true method to make the solution matter.
Whatever method you use, just remember that the main character’s goal in solving the crime must be a strong and worthy one, and the emotional reasons for the solution must matter to both the reader and the detective.