FBI agent Ross Rice said that the new information in the Zywicki case "is being investigated right now," but that he could not "characterize the tips, because that would be unfair to the people who came forward. We also can't say if they will or will not be helpful until we complete the investigation."
Zywicki was returning to Grinnell College in Iowa in 1992 when she disappeared. She had stopped her car on Interstate 80 near La Salle, Ill.
Nine days later, her body was found 500 miles away, on Interstate 44 near Joplin, Mo., wrapped in a blanket that was closed at both ends with duct tape. She had been sexually assaulted, and stabbed eight times.
In the Laurite killing, the victim, who was traveling along Interstate 40, pulled over at a Morrilton, Ark., rest stop and was fatally stabbed.
Zywicki's mother, JoAnn Zywicki, 63, now of Ocala, Fla., said she was encouraged to know that - as with Laurite - her daughter's case had not been forgotten, and that it was being actively investigated 13 years later.
"At this time of the year," when school starts again, "I can't help but think about it," said Zywicki, who lives in a retirement community with her husband, Henry, 65, a former civil engineer. "I put it on a back burner, but I still think about it.
"They say time heals - but it doesn't. It's the idea of not knowing. It always hangs over you."
Zywicki said the FBI told her this month that evidence found with her daughter's body was insufficient for DNA typing. FBI officials have declined to say whether they had enough for typing.
Zywicki and Martin McCarthy, a former master sergeant and special agent in the Illinois State Police who investigated the slaying before his retirement in 2002, have criticized authorities for not actively pursuing leads in the case.
They also have called for a grand jury to be convened to question people who were interviewed by authorities in the early investigation.
"I would feel better if I thought they connected all the dots," Zywicki said. "This has been like one of Tammy's puzzles. She always had an unfinished one on the cardboard - and would stick it under the sofa. Maybe this puzzle will be finished."
McCarthy, 58, of Wheaton, Ill., said he believed investigators were very close to learning what had happened more than a decade ago.
"I'm not saying who killed [Tammy Jo Zywicki] - just that there is a hell of a lead," he said. "It's the most frustrating thing."
McCarthy said a nurse driving on Interstate 80 had seen Tammy Jo Zywicki standing at the rear of her car. A green pickup truck had pulled over, and its front faced the front of Zywicki's car. A man stood next to the truck and appeared to be assisting the student.
McCarthy said the nurse - after learning of Zywicki's disappearance - later recognized the man, Lonnie Bierbrodt, when he came to her office with his wife, who was having blood tests done.
The wife, Carrie Bierbrodt, pointed out a musical watch she said her husband had given her - one similar to a watch missing from Zywicki's belongings, said McCarthy.
Lonnie Bierbrodt was interviewed by investigators, who determined that he owned a green pickup, was originally from the La Salle area where the victim was last seen, and lived near the location where the body was found, McCarthy said.
Bierbrodt, who had served time in prison for attempted murder and armed violence, died in 2002, the former investigator said.
Authorities said they never had enough evidence to charge anyone in the case.
But McCarthy and Zywicki said more information could still be brought out by questioning the nurse, Bierbrodt's former wife, and others before a grand jury, under the threat of perjury charges.
"I have waves of grief," said Zywicki. "It just hits you. One of Tammy's favorite songs was Tom Petty's song 'Free Fallin' ' - we played it at her funeral.
"Many times I'm in a store and it comes on, and I'm reminded again. These things don't just happen and go away."
Contact staff writer Edward Colimore at 856-779-3833 or email@example.com. To comment, or to ask a question, go to http://go.philly.com/askcolimore.