They're the cases that can haunt local law enforcement for years, even decades, they're cold cases.
When a murder goes unsolved, there's a void left for officers and the families of the victims.
"There are a lot of families of victims who are still traumatized over this. The issue doesn't go away because the case can't be solved, they never have closure", said Wisconsin Attorney General J.B. Van Hollen.
The Attorney General takes pride in the partnership between the Department of Justice and local police forces in working to solve cold cases. He says the most important tool in accomplishing that, is DNA technology, which can quickly change a case from cold to closed.
"DNA is almost foolproof. It will convict somebody with almost certainty or acquit someone with almost certainty and so it's a tremendous tool, probably the best that has ever come along for law enforcement", said Attorney General Van Hollen.
In 2009, James Emerson was sentenced to life in prison for the murder of Rhonda Mertes, ten years after she had been killed in downtown Wausau.
That conviction came as the result of DNA evidence and a tip, after a cold case report aired right here on Newschannel 7.
Since taking office in 2007, the Attorney General Van Hollen, has brought renewed focus to solving cold cases.
In September of 2010, Van Hollen secured a half million dollar grant from the U.S. Department of Justice to help pay detectives overtime to work specifically on cold cases.
In July of this year, the Department of Justice released a deck of cold case playing cards, with pictures of the victim's faces and descriptions of the crimes.
Less than a month ago, the attorney general unveiled a new state web-site that focuses on supporting the families of cold case victims. It provides information to help families interact with law enforcement and cope with the emotional toll of an investigation.
"A lot of people forget, in the criminal justice system what it's all about and it's about victims. These cold case families of victims, after the case is closed and it's gone cold, people kind of forget about them and they don't really get the services anymore, they're not front and center", said Van Hollen.
Tune in to Newschannel 7 tonight at 5, 6, and 10 for a closer look at what the state and local law enforcement agencies are doing to work cold cases.