Unidentified officials spoken to by The Times (U.K.) in October 2001 expected that the bodies of the 9/11 suspects would be identified "by a process of elimination'. They did not explain why they did not expect a positive identification of these bodies.
Chris Kelly, spokesman of the Armed Forces Institute of Pathology (AFIP), where the identification of the victims' remains from flights AA77 and UA93 took place, said that the authorities were reluctant to consider releasing the hijackers' bodies: "We are not quite sure what will happen to them, we doubt very much we are going to be making an effort to reach family members over there.' He did neither explain why no efforts would be made to locate the families of the alleged hijackers, nor why AFIP could not use comparison DNA samples from known locations in the United States where the alleged hijackers had lived. According to Llonald Mixell, landlord of one of the alleged hijackers, Alomari, in Vero Beach, Florida, the FBI "searched the Omari home [and] agents left a list of materials seized, including hair samples and air conditioning filters." According to Jeff Killeen, spokesman for the FBI field office in Pittsburgh, "there haven't been any friends or family members to try to claim to remains of [the hijackers]."  Yet the family of alleged hijacker Ziad Jarrah in Lebanon was reported as early as September 16, 2001, to be "ready to cooperate with the authorities." They did not believe the allegation that Ziad was a terrorist. The US authorities did not respond to this offer of cooperation. In mid-August 2002, a new report on the victims' remains noted the DNA still had not been checked, because "little attention has been paid to the terrorists' remains." While the AFIP announced to have positively identified the human remains of all "innocent' passengers and crew from the flights, they did not identify the remains of any of the alleged hijackers. Kelly said later: "The remains that didn't match any of the samples were ruled to be the terrorists'.  Somerset County coroner Wallace Miller said that the "death certificates [for the suspected hijackers] will list each as 'John Doe'". 
Among documents transmitted to the 9/11 Commission and released in 2009, one document contains the claim by the FBI that DNA profiles provided by the German Federal Police (BKA) to the FBI from Ziad Jarrah's girl friend in Germany (Aysel Sengun), "matched the sample of one of the sets of unknown human remains".  The document was found at the National Archives by History Commons contributor paxvector, and posted at the History Commons site at Scribd.
Actually, the aforementioned statement does not explicitly say where the "unknown human remains" were found, but merely implies by juxtaposition with another paragraph that these remains were found at the crash site of Flight UA93 in Pennsylvania.
The FBI claim, just recently discovered, cannot be considered as a proof that Ziad Jarrah participated in the crime of 9/11. First, even if Ziad Jarrah had actually died at the crash site, it would not necessarily imply that he piloted the crashed aircraft. Other evidence would be needed to substantiate such an allegation.
Secondly, the FBI document in question was not signed, dated or otherwise authenticated. It was not either accompanied by a chain-of-custody report that would document the integrity of the specimen from the point of collection to the final results. The legal status of this document is therefore inconclusive. Additionally, four distinct reasons regarding the alleged crash of Flight UA93 converge to throw doubt on the claim that a passenger aircraft actually crashed in Pennsylvania:
(a) Local residents who rushed to the crash site at Shanksville reported to have been surprised to see no signs of an aircraft crash, no jet fuel smell, no bodies, just a hole in the ground.  According to Assistant U.S. Attorney General Patrick A. Rose, representing the FBI, no attempt was made by the FBI to formally identify the aircraft. The justification he provided was that "[t]he identities of the airplanes hijacked in the September 11 attacks was never in question."
(b) According to the FBI, about 95 percent of the aircraft was recovered from the crash scene.  The FBI did not forward the wreckage to the National Transportation Safety Board for a mandatory crash investigation but "since [it] had no more use for it', turned it over, 12 days after the crash, to United Airlines . Photographers were not allowed to document the recovery of the aircraft. No photographs of the recovered wreckage exist in the public domain.
(c) After weeks of combing the area, searchers found "about 1,500 mostly scorched samples of human tissue totalling less than 600 pounds' or about 8 percent of the total combined bodily weight of the aircraft's passengers, crew and hijackers.
(d) The Armed Forces Institute of Pathology (AFIP) carried out the identification of the victims from the crash of flight UA93 after a "behind-the-scenes tug of war' between the FBI and the Virginia Chief Medical Examiner, Dr. Fierro, whose department was legally responsible for such work.  Attorney General John Ashcroft had to formally relieve her department of its responsibilities in this case.  It was never explained why it was crucial to have such identifications conducted under the authority of the armed forces.
A detailed and throughly documented study by Paul Thompson suggests that there were actually more than one Ziad Jarrah.  In that case, the very identity of the alleged hijacker Jarrah would be questionable. For the present purposes, the alleged identification of Ziad Jarrah's remains must be considered as dubious, particularly because no other evidence corroborates the boarding of the aircraft.
As for the remains of the suspects who allegedly flew AA11 and UA175 into the Twin Towers, a spokeswoman for the New York Medical Examiner's Office, where the identification of the WTC victims took place, said to have received from the FBI in February 2003 "profiles of all 10 hijackers ...so their remains could be separated from those of victims." She added: "No names were attached to these profiles. We matched them, and we have matched two of those profiles to remains that we have." In 2005, the number of matched samples increased to three.  Robert Shaler's medical examiner's forensic unit in New York could not identify the three by name. "No names, just a K code, which is how the FBI designates 'knowns,' or specimens it knows the origins of," Shaler wrote. "Of course, we had no direct knowledge of how the FBI obtained the terrorists' DNA." His statement was echoed later by his deputy, Howard Baum: "We had no idea where the profiles came from or how they were developed." In 2009, Newsweek interviewed again Rober Shaler and others who continued in their efforts of identifying victims of 9/11 and the remains of the "hijackers". Yet, in spite of these efforts, "1,126 of the 2,751 victims from the World Trade Center and five individuals from the Pentagon have yet to be identified at all--none of their remains and no traces of their DNA have been found."
No explanation was given where and how the FBI secured the "profiles" of these 10 individuals, why it took so long to hand them for identification and why they could not be identified by name. It is important to remember that according to the official account the alleged hijackers left numerous identifying documents and artifacts (see introductory section of this essay) including personal items, that were "luckily" found by the FBI, and from which DNA comparison samples could have been extracted to permit at least the positive identification of some of these individuals.
On August 18, 2009, the New York Times reported that that it is possible to "fabricate DNA evidence, undermining the credibility of what has been considered the gold standard of proof in criminal cases." According to this report, scientists in Israel "also showed that if they had access to a DNA profile in a database, they could construct a sample of DNA to match that profile without obtaining any tissue from that person." For law-enforcement authorities to fabricate DNA evidence demands, obviously, that experts willingly participate in serious crime and risk thereby long prison sentences, if found out. This may explain why no attempts were made to fabricate DNA evidence in order to prove the presence of bodily remains of the 19 alleged Muslim hijackers at the crash sites.
The lack of positive identification of the alleged hijackers' bodily remains, compounded by the lack of an established chain of custody of these remains, means that the US authorities have failed to prove beyond reasonable doubt that the alleged hijackers died on 9/11 at the known crash sites.