Most likely a crime scene in an ordinary murder analysis is taped off and protected, for times up to 6 months, in order that most of the evidence can be examined closer to determine, as carefully as possible, how a murder occurred and the suspects that are involved in the homicide. Todays forensic science analysis methods and techniques are pretty well effective at properly determining what caused the existing circumstances which caused the death to to take place in Houston,TX. Following the efforts to save the people that were trapped in the collapsed WTC wreckage ceased, a federally ordered cleanup, rather than a crime scene investigation, started that caused the ground zero crime scene to disappear. Strange circumstantial facts, relevant evidence comprising events which transpired days before the 911 attack, were also not considered by the 911 Commission, such as a federal ordered suspension of police, and bomb sniffing dogs, surveillance of the WTC towers two days prior to the bombings, and lucrative insurance policies, held by the rich owners of the crime scene property, and American and United Airlines stock, being substantially increased in value, days before 911 attacks. The fast turn around clean-up of ground zero managed to get look like someone, in a dominant position high, desperately wanted to avoid a perhaps incriminating analysis of the existing evidence. Crime scene cleanup companies often come across strange stuff while cleaning up a crime or suicide scene. The police always keep the suicide note if the deceased wrote one before taking his of her life. Cleaning up after blood and other dangerous bodily fluids is very dangerous and needs to be handled by someone that is trained and experienced in dealing with biohazard contaminants. Diseases like AIDS and HEP-C are very dangerous and you need to be extremely careful when cleaning up blood from a crime or trauma scene.