There was a long discussion on the use of search dogs starting at the bottom of the page on this thread:
http://www.websleuths.com/forums/showthread.php?234651-Lloyd-Welch-is-Person-of-Interest/page13
But the summary (according to my memory, not checked) is:
In 1975 Montgomery County did not use or bring in their own search dogs as far as we know.
One eyewitness placed the girls walking back to the mall at 6 or 7 PM, so the police during the first week did not concentrate on the path; the initial police search concentrated on the plaza (now mall) and Tape Recorder Man, although people did search everywhere, spreading their effort out. A week later, for unknown reasons, the police thought this eyewitness, a young teenager seeing the girls at dusk, was mistaken as to seeing the girls walking back to the mall; he could be off by a day or just mistaken.
A week after the abduction, two more teenagers came forward and said they saw the girls walking down Drumm Ave ....
... @Richard. If Cadaver dogs can sometimes smell bodies 40 years after the burial, as they were used in the VA search warrant, to cover all bases, should't the police walk cadaver dogs around the mall and nearby Wheaton, Kensington just to be sure?
...
Steve,
Excellent summation of, and links to, previous posts on the subject of the girls' walk to and (possibly) from Wheaton Plaza on 25 March 1975.
Your mention of some of the eyewitnesses and police evaluation of their testimony is an interesting topic for consideration. Police and news media (in 1975) identified or mentioned about 10 specific persons who stated that they had seen the girls that fateful day. Except for a retired woman in her 60's (who knew the girls personally and recognized them), all other witnesses were between the ages of 12 and 18 years old.
A big question that I would have for MCP is whether or not they ever re-interviewed any of those young eyewitnesses after 1975. As you point out in your post, Police seem now to think that the girls were abducted in the close vicinity to Wheaton Plaza and never made it "back to the path" (ie their usual walking route) home.
Individual MCP investigators have waffled back and forth over the years regarding the afternoon Drumm and Devin sighting, some have expressed doubts about it, but they have never officially stated that it did or did not occur.
The statement of a 12 year-old boy who was mentioned in the first MCP press briefing of seeing them around 7:30 PM on Tuesday, 25 March 1975, was (by 28 March 1975) in a subsequent press briefing officially discounted because police believed that his information did not "fit" with what they thought they knew at the time.
That boy was a classmate of Sheila's and he knew both girls by sight. He was identified by name and interviewed by a Washington Star reporter in the early days of the investigation. As an adult, he has maintained that he saw them on Faulkner Ave in Kensington on that day.
Monday, 24 March 1975 was cold and rainy all day long, and it was stated in news accounts at the time that the girls did NOT go to Wheaton Plaza, but rather had stayed at home that day.
That "7:30" sighting has always been a puzzle to me. Did the boy actually see them that evening heading TOWARD the Mall? Or was he misquoted/misunderstood? If he had seen them in the morning of 25 March, headed toward the Mall, it would have been about 11:30 AM. Did MCP even bother to re-interview him before publically discrediting his story? By 7:30PM, it had been dark for over an hour.
In regard to search dogs... I have covered this subject in other posts, but you are correct to state that the Pennsylvania german shepherd tracking dogs were the first and only ones brought in to search - a full week after the girls disappeared.
It was stated that the dogs "alerted" on the girls' scent near a ditch or drain somewhere near the Kensington swimming pool. Photos that I saw of the dogs and handler showed them walking down residential streets, but I do not believe that the dogs were actively following a track at the time. They were brought back the second day and taken to the wooded area and other areas near the girls' home, but according to reports did not find anything.
Those were TRACKING dogs, which were specifically trained to smell a sample or target scent (possibly a pillow case, piece of unwashed clothing, etc) and then attempt to pick it up. Once a scent is found by the dog, he will take you on the path that the person walked.
From my understanding of police briefings on the subject - and from my own personal experience as a tracking dog trainer/handler - I do not think that those dogs ever found a track to follow. It is possible that they might have found a faint residual scent trace in a protected area, where it could not dissipate, but as MCP reported at the time, they could not tell when it was left there. It could have been from their trip TO the mall rather than to their home, as there was no track or direction of travel noted.
Cadaver Dogs are used to locate dead people, usually buried under soil, debris, or even in the water. They can detect such scents even years after death - if conditions allow for it. If a person is buried, covered, or in some way preserved, the dog has a better chance of alerting. But if a body had only been stored, or laid briefly in an open place, the scent would have dissipated within a fairly short time, depending on such factors as temperature, wind, rain, disturbance of the area, etc.
Cadaver Dogs are primarily trained to detect any dead human, rather than to go for a specific human scent, as is the case with tracking dogs. I doubt that using them in the Kensington area would be of any use today.