The knife found piercing the chest of 27-year-old Philadelphia teacher Ellen Greenberg has never been fingerprinted, according to the attorney for her parents, who are suing city officials over an alleged coverup of her murder.

Greenberg was discovered dead in her kitchen in January 2011 with 20 stab wounds, including 10 from behind.

But city authorities have said for years that her death was a suicide and are still embroiled in a court battle over evidence in the case, which her parents want access to. One piece of that evidence is the knife itself.

PHILADELPHIA TEACHER'S SUSPICIOUS SUICIDE CRIME SCENE WAS CLEANED UP BEFORE POLICE ARRIVED WITH SEARCH WARRANT

Ellen Greenberg in Penn State hoodie

A younger Ellen Greenberg smiles in an undated photo provided by her childhood friend and Penn State classmate. (Erica Hamilton)

"We would like to have it tested, minimally, just to see if there are fingerprints on it, because if there aren't any fingerprints, that says a lot," said Joseph Podraza, the attorney for Joshua and Sandee Greenberg and their daughter’s estate.

It would mean someone — a potential killer — wiped them off after she was dead, he told Fox News Digital.

"And if there are fingerprints other than Ellen's on that knife, well, that says a lot too: Somebody clearly did stab her," he said. "And it's never been fingerprinted."

WATCH: Nancy Grace investigates the mysterious 'suicide' of teacher Ellen Greenberg on Fox Nation

ELLEN GREENBERG ‘SUICIDE’: PENNSYLVANIA COURT HEARS ARGUMENTS IN FAMILY'S BID TO OVERRULE MEDICAL EXAMINER

A computer illustration showing some of Ellen Greenberg's knife wounds

A computer illustration showing four of Ellen Greenberg's knife wounds to her head and torso. (Tom Brennan)

Dr. Michael Baden, a renowned forensic pathologist who is not connected to the case, said if the knife has been stored properly all this time fingerprints can be analyzed. 

"Fingerprints usually don't go away unless they are wiped away," he told Fox News Digital. "If the knife has been properly preserved, a foreign fingerprint might still be findable."

A lot of evidence in the case deserves scrutiny, according to Podraza and the family's private investigator, Tom Brennan.

Despite collapsing with nearly two dozen stab wounds in a bloodstained kitchen, Greenberg was found clutching a "pristine" white towel in her left hand, the lawyer said.

A rendering showing more than a dozen of Ellen Greenberg's stab wounds

A rendering showing more than a dozen of Ellen Greenberg's stab wounds. (Tom Brennan)

"I think that that towel that's in her left hand was used to wipe it (the knife handle)," Podraza told Fox News Digital. "And I think that somebody may have come upon the scene quicker than they thought, and that's how that towel ended up in her left hand."

Why a 2011 'suicide' case could be investigated again: Dr. Michael Baden

"How many people are cutting up fruit for a fruit salad to eat for lunch, then decide, 'Oh, you know something, I'd rather kill myself now?'" Podraza said. "'So let me go get a white towel, hold it in my left hand while stabbing myself 20 times to death.'"

Last month, a panel of appellate judges ruled against the parents' request to force the Philadelphia medical examiner to reclassify Greenberg's death from suicide to homicide or undetermined. 

But the panel also slammed the city, police and the medical examiner's office for the investigation.

Ellen Greenberg smiles in an undated photo

Ellen Greenberg smiling in an undated family photo provided by her mother, Sandee Greenberg. Ellen was found dead at the age of 27 with 20 stab wounds, half of them to the back of her head and neck, in a gruesome death that Philadelphia authorities ruled a suicide. (Sandee Greenberg)

"The facts surrounding this matter are extremely disturbing and the Parents’ tireless efforts over the past 12 years to learn exactly what happened to their daughter on the evening of January 26, 2011, warrant our sincere sympathy," Commonwealth Judge Ellen Ceisler wrote in the majority opinion. 

"The experts they enlisted have all raised serious factual questions about Dr. [Marlon] Osbourne’s and Dr. [Sam] Gulino’s conclusions, and even the [medical examiner's office] now concedes that there 'is no dispute that evidence in the record could support other conclusions about the manner of death.'"

Josh and Sandee Greenberg sit across from Nancy Grace

Parents of Ellen Greenberg talk to "Crime Stories" host Nancy Grace for new Fox Nation show.  (Fox News)

PHILADELPHIA SUICIDE DESIGNATION FOR WOMAN WITH 20 STAB WOUNDS, BRUISES, IGNORES HOMICIDE EVIDENCE: EXPERTS

Ceisler outlined glaring flaws in the investigation. Osbourne's initial finding was that the death was a homicide, but his determination came after the crime scene had been cleaned up and before police arrived with a search warrant. 

And Dr. Cyril Wecht, a famed forensic pathologist who conducted an independent review of the autopsy, found the evidence "strongly suspicious of homicide" and "noted that the investigators made no effort to examine the knife found in the Victim’s chest for fingerprints," she wrote.

A separate judge is expected to hear oral arguments on the family’s request for evidence in the case as part of a separate lawsuit alleging a conspiracy to cover up a murder. The city is actively fighting against the disclosures.

A damaged sling latch above an undamaged door lever

According to authorities, the door to Greenberg's apartment had been kicked in from the outside while bolted shut. A photo taken at the crime scene shows the latch attached on both sides, which Greenberg's family says makes that version of events impossible, arguing it should have broken off from either the door or the frame.  (Tom Brennan)

Officials have said they cannot answer questions directly related to the case, citing the pending litigation and an ongoing outside investigation in the hands of the neighboring Chester County District Attorney’s Office.

A Philadelphia spokeswoman told Fox News Digital last month the city was "pleased" with the appellate ruling in its favor.

"The city is now, and has always been, deeply sympathetic to Joshua and Sandra Greenberg's pain and deep grief over the loss of their daughter," she said in a statement. "If Mr. and Mrs. Greenberg have new evidence about their daughter’s death, we urge them to present it to the investigators in Chester County, as they have the authority to reopen the investigation."

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Dr. Marlon Osbourne, the former assistant Philadelphia medical examiner, has not responded to emails or phone messages. He continues to work as a forensic pathologist and is an associate medical examiner in Palm Beach, Florida.

The parents plan to appeal last month's appellate decision to the state's Supreme Court, Podraza said, which he called "a road map" on how to get away with murder.

"That's the most astounding aspect of the opinion. You have, as I read it, three judges saying this young woman was murdered. The investigation is grossly flawed and embarrassing. There is a murderer or murderers out there. But our hands are tied, and nobody can do anything except the government officials, and you're therefore subject to their whims," he told Fox News Digital.