Here is what I found in the mainstream accounts about the A-frame. First, Maribeth Conway, in Part IV of the "Maura is Missing" series. She starts out by observing that Fred Murray took the opportunity to get permission to search the house once it went up for sale--so this was not a LE search, from the beginning.
On the first day, a cadaver dog searched the house and had hits on the second level; the next day four more cadaver dogs were put to work in the house and went "bonkers," Fred said. The strongest hits by the dogs were in a downstairs closet. Cadaver dogs are skilled in sniffing for decomposing bodies but are not able to distinguish the identities of bodies. 

Though a dead body could have been stored in this closet, the dogs were not capable of identifying if the body was Maura.


The investigators took a few trash bags filled with items from the house and a piece of carpet from the closet. According to Fred, the carpet was to be divided into two pieces: a portion of the carpet was to be given to state police, who were not present for the search, and the other portion was to be held by the group of volunteer investigators. A medical laboratory examination was to determine if stains on the carpet were blood, and if available DNA matched Maura's. Seven months later, laboratory test results have not been made available from either group.


There is confusion over who has custody of the carpet. Private Investigator Healy was ill the weekend of the search, but said that police were not at all interested in the evidence and would not take the carpet into their possession. Healy said the carpet is in the custody of an investigator who no longer "has business relations" with the group.
http://southshorexpress.com/extras/special-reports/81-maura-is-missing-part-iv-the-aftermath.html
The SOCO article also covers this aspect of the search, but sites Fred as the source of information that the carpet samples were never tested for DNA.
Murray recalls that carpet samples were taken from the house and were supposed to be tested for DNA. The samples were never tested, he said, and the leader of the private investigative group didn’t tell the state police about the samples until two and a half years later
Clearly, there have been no briefing from LE to the media or the general public about these carpet samples (as to DNA, blood type, or source of the blood stain). It is indisputable that dogs hit on a scent, and Conway says they were "cadaver dogs," which are NOT looking for blood (menstrual or any other kind) but as anyone who watched the Casey Anthony trial can tell you, are trained to hit on the scent of
human decomposition. The purpose of testing supposed blood stains in the closet was to see if Maura's DNA was present, which would have linked her to the A-frame, and presumably to its occupants.
http://www.mauramurraymissing.com/
Now, we don't know what is going on with the carpet samples. Healy says the state police wouldn't take them, which makes a kind of sense since they weren't evidence collected officially. If they are still out there somewhere, presumably they could be tested for DNA, still, if anyone knows where they are. What no one knows is what kind of blood, if any, or whose DNA, is on the carpet samples. There were supposedly two samples. One should be with the "volunteer investigators," and the other was to go to state police, who reportedly refused to take the sample. So where is it? And if all of this is in private hands, surely it could have been tested. But NONE of this confirms the rumors noted above that the blood (on a carpet, in the closet) was from a clothes hamper (which is a simply ludicrous story).
