By Suzanne Le Mignot

(CBS) — They have one goal: to use their vast resources to investigate cases that have gone cold.

CBS 2’s Suzanne Le Mignot shows us the work of the Chicago FBI Cold Case Homicide Squad.

“It’s just not fair, you know,” says Sandra Anaya.

She is the mother of Alexandra Anaya.

In 2005, the 13 year-old’s torso was found floating in the Little Calumet River. It was bound with chains.

“Just the fact that this poor little girl was murdered in such a brutal way and dismembered, is shocking to all of us,” says Michael E. Brown, the Supervisory Special Agent who heads the Chicago FBI’s Cold Case Homicide Squad.

CBS 2 observed the squad’s weekly meeting and agreed to shield the identity of the agents. On the walls: some of the 20 crimes they are investigating.

“Some cases we have might be a year old. Some might be over 40 years old,” Brown says.

The squad works on cases with local law enforcement throughout Chicago. Partners include the Chicago Police Department.

James Sherlock, a Chicago police detective, is part of the recently formed unit. He’s the lead investigator on the Anaya case.

“There are families of these victims and these families, they’re in the shadows, and they’re waiting for something to happen,” he says.

A recent tip has agents working on the Anaya murder case. Video shows FBI and CPD divers last October in the water, where the teen’s body was found, more than a decade ago.

“To think that this person who committed this crime is still out on the street is a huge motivating factor for us to do everything we can,” Brown says.

Sandra Anaya is grateful police are still searching.

“It makes me feel that they haven’t forgotten — you know, after all these years, that I’m not the only one that still cares.”

The Chicago FBI is asking anyone who knows anything about the murder of Alexandra Anaya to call them at 312-421-6700. You can remain anonymous.