The killer's DNA is the Holy Grail of the Holly Cassano case.
Semen and the killer's blood were recovered from the crime scene. Champaign County sheriff's detectives believe he was likely cut as his hand slid over the hilt of a kitchen-type knife.
DNA was extracted from both samples to develop profiles that are unique only to the contributors of that blood and semen.
"It's obviously huge and puts us in a good position," said Lt. Curt Apperson, who is supervising detectives investigating the crime. "We feel every day we're going to solve this case."
None of the detectives is prepared to adopt one theory of what happened over another, despite the input of an FBI profiler who suggested the killer may have been a white male, possibly a teenager, who may have expressed sexual interest in Holly Cassano and may have been "acquainted" with the mobile home park.
Apperson said it's "dangerous" to stick with a single prevailing theory.
"You need to keep an open mind. Each door that opens, each tip we get, is another theory or another opportunity or scenario," he said.
"We just hope it is not somebody who is already deceased," said Sgt. Dave Sherrick, a sheriff's deputy who spent fours years on the case as a detective. "In the back of my mind, there's always the possibility that the DNA may not show up. It's a big piece of evidence that can't be refuted."
Dwayne Roelfs, the current lead case agent, said the detectives followed the suggestion of the profiler to hone in on the mobile home park and the immediate vicinity. They went door to door in the park, which is more than a mile long, he said.
But like all neighborhoods, there's a lot of movement.
"You just keep looking and hoping that something will come up. From time to time, you get something that looks promising and it turns out it's not. That's the tough part of the job."
Roelfs developed a spreadsheet with the names of the more than 100 people interviewed.
"For the most part, we know all the main players — the relatives and close friends. Any time a name was mentioned, we put it on the spreadsheet to see if the name had come up before and the reason for it. We associated a date with the name. The reports are in chronological order so we can go to that date and find the report," Sherrick said.
The spreadsheet also indicates if a DNA sample was taken from a person and if it's been run through state and national databases for comparison.
Just last week, Roelfs took another cheek cell swab from a person to compare his DNA to the killer's.
Every time he approaches a new potential suspect or witness, he gives a brief explanation of the crime and shows Holly's picture.
"We're looking for their reaction," he said.
And when the detectives explain that a DNA sample can eliminate them from suspicion, most are cooperative.
Sherrick continues to remind people, especially in the Candlewood Estates park and around Mahomet, that they're still investigating Holly's murder. Despite shifts in assignments, Apperson said, "the one thing that's consistent is that the energy on this case remains high."
Yet another detective was recently assigned to review the evidence, "putting fresh eyes on it to make sure we're not overlooking something," Apperson said.
— Holly Cassano, 22, was found dead in her home at 298 DuPage in the Candlewood Estates mobile home park, northeast of Mahomet, at about 10:30 a.m. on Nov. 2, 2009.
— She was last seen alive around 10:15 p.m. the night before at Meijer in Champaign, where she was a cashier. She had also recently held a second job at the Bob Evans Restaurant in Champaign.
— At 11:20 p.m. she texted her mom, who was watching her 17-month-old daughter, then popped in a DVD and fell asleep. Her mother found her the next morning after being unable to reach her by phone. The door was ajar, and the TV was still on.
— Investigators believe her killer was also cut in the attack; his blood and other DNA evidence were found at the crime scene.
— An FBI profiler suggested the killer may have been a white male, possibly a teenager, who may have expressed sexual interest in Holly and may have been familiar with the mobile home park.
— Detectives focused their investigation on Candlewood Estates, which has more than 500 mobile homes and is heavily transient.
— More than 100 people have been interviewed; dozens of DNA samples have ruled out all potential suspects so far.