http://www.k9fleck.org/sar/cadaver_dog.html
The Federal and State case law states that when one of these types of dogs alerts to or locates human odor, that alert is only one reasonable suspicion indicator.
Reasonable suspicion is defined as a "particularized and objective basis for suspected legal wrongdoing". In this case, the wrongdoing may be a suspect, a track or trail of a suspect or scent line up.
The dog alert is simply one indicator of wrongdoing. Now, the peace officer in charge of the case must develop other reasonable suspicion indicators to develop probable cause. "Probable cause exists when under the totality of circumstances known to the arresting officer; a prudent person would have concluded that there was a fair probability that the defendant had committed a crime."
These other reasonable suspicion indicators may be direct or circumstantial evidence.
The bottom line to a human scent K-9 handler is this; the dog alert must be corroborated by other evidence.
Kerr v Lyford (171 F.3d 330 U.S. Court of Appeals Fifth Circuit, 1999)
The court found probable cause in this case, based upon these reasonable suspicion elements:
Statements of the child witnesses implicating the Kerrs in their own sexual abuse and in Wilson's abduction, rape and murder;
Medical examinations of the children that revealed scarring consistent with their tales of sexual molestation;
Confessions and statements supplied by adult witnesses Geer, Martin, and Wanda Kerr, verified by polygraph, consistent with those of the children in implicating the Kerrs in the kidnapping, rape, and murder of Wilson;
Corroborative physical evidence such as masks, knives, and other instrumentalities of restraint and torture that were referred to by the children;
An infrared scanning device and a cadaver-sensing dog suggested the presence of human remains on the Kerr's property, and bones (albeit not conclusively human) were unearthed;
The shed in the Kerrs' backyard--which had been identified by some of the children and the adults as the place where Wilson's body had been kept--was also alerted to by the dog and, suspiciously, showed signs of recent washing and repainting.
IMO....the disturbed soil in the Anthony's back yard, and cleaning of the car creates probable cause. Now, wait for the defense to attempt to get the car thrown out entirely.
As YM is an experienced homicide detective, the smell itself would have been a big UH OH that needed following up on.