CHICAGO -- Investigators in the case of two missing girls, Diamond, and Tionda Bradley, told Unit 5 reporter Renee Ferguson that their search has been exhaustive. They say the search has included police and FBI agents from Mississippi to Morocco and many places in between. They have followed up on 640 leads. They've worked with preachers, psychics, and private investigators. And there's a $30,000 reward for the person who finds the Bradley girls.

Diamond was 10 and Tionda was 3 at the time of their disappearance last July 6.

The girls' mother told Ferguson that her daughters' voices haunt her dreams.

"It's hard, I hear them crying for me. They want to come home," Tracey Bradley said.

After nearly 11 months of searching, Chicago Police Lt. Dalia Padgurskis said she has reached some conclusions about the case.

"These girls did not disappear on their own," Padgurskis said.

Padgurskis heads a task force that has its own command center at police headquarters. As Padgurskis showed Ferguson a disappearance time line on one wall, she said, "We'd also like to talk to the grandfather."

On another wall is a drawing by the Bradley girls' sister that detectives tacked up to motivate them. There are stacks of boxes around the office that hold files of thousands of interviews and hundreds of hours spent searching.

"(We've searched) every known location, any possible hole, any possible pile of wood or basements in the area or abandoned buildings, and we're very comfortable that it's not an accidental missing," Padgurskis said.

Padgurskis said nobody has been ruled out as a suspect. Even after pursuing nearly 640 unsuccessful leads, she said she's not ready to say the case is cold.

"We still have a number of leads that we're pursuing," Padgurskis said. "We haven't closed every avenue yet. And until we do that, we're going to keep at this case."

Private investigator Jim Miller is still searching, too. He and his partners now work the case for free.

"We get information that the girls are dead. We get tips that they are alive. I got tips that they are in Mississippi. I get tips that they're in Minnesota," Miller said.

The case also took investigators to Beloit, Wisconsin, along the Rock River, this spring. The Bradley girls' great grandfather, Eugene Bradley, lives nearby. He told Ferguson that police and FBI agents searched his home, but he didn't mind.

"I'll tell you why," Bradley said. "It's because once you eliminate me and know that I ain't involved, you can quit messing with me and go find my babies. That's what I want them to do."

Ferguson said that one of the latest police theories was that the girls were taken to North Africa by an Arab man who was forced to pay child support for one of the girls until last summer, when he learned he was not the child's father. FBI agents went to

Morocco looking for the girls but found nothing.

Another theory, Ferguson said, was that the girls were abducted by a serial killer thought to be in the area at the time.

Investigators say they're sure that if 11-year-old Tionda could call home, she would.

"If she is alive and not able to do that, then it's because she's out of the country," Padgurskis said. "And, of course, we are all in fear that they may, in fact, be dead."

Monthly vigils have kept media attention on the girls' disappearance. Ferguson reported that Tracey Bradley has a team,

including attorneys and community activists, that tries to keep interest in the case as the one-year anniversary approaches.

"Now there is a need for the public to embrace helping us find these children," said team member Rev. Paul Jakes of Old St. Paul's Church.

Ferguson said Bradley admits that as time passes, belief and hope give way to despair and an unanswered question that gets asked over and over again: Where are Diamond and Tiffany?

Ferguson said Unit 5 sources told her that when the FBI went to Morocco, the agents were not allowed to conduct any actual investigation themselves. Local authorities, they said, did all the checking that was done.

Police told Ferguson that the girls' mother has not always been cooperative, but she is not considered a suspect in the case.

Anyone with information is asked to call Chicago police. There is a Web site -- BradleySisters.com -- for tipsters to provide information anonymously.