IIRC, the initial responding officers started CPR after GZ was disarmed. Paramedics arrived soon after, and took over the CPR and trauma assessment of TM. In that process, they would have exposed his chest for purposes of evaluating the location of the GSW entry site, as well as using a cardiac monitor/ defibrillator to evaluate cardiac function. (Among many other activities occurring simultaneously.) Exposing the chest and evaluating the extent of cardiac electrical activity is a necessary initial step for paramedics, and is included in well-defined, very detailed EMS protocols, and is also necessary to establish documentation of asystole for pronouncing death at the scene. I am betting that the paramedics in this instance were also in continuous contact immediately with the ER docs, and once the full evaluation was communicated (GSW location, response to CPR, asystole, etc), they were given permission to suspend lifesaving efforts and pronounce at the scene.
So, there is likely a couple of ways Detective Gilbreath could have learned about the stippling on the body, from a source other than the autopsy report (which will include descriptions of the entry wound.)
Gilbreath probably has read the "run report" medical record produced by the paramedics, which probably included that detail. He likely would also have talked directly to the paramedics and officers who were there, and heard them describe the "stippling" that is characteristic of a close range GSW. Possibly also spoke to docs and nurses who were in communication with the paramedics at the scene.
I'd also add, it's worth remembering that CPR cannot be effective is there is no intact heart and/ or great vessels. CPR will not produce a pulse in this situation-- the heart is empty. CPR relies on a closed "central" system to move blood with compressions.
All of the best CPR in the field cannot save someone with a shredded heart, and/ or great vessels, who is in asystole. That is why he was pronounced in the field, and not given CPR and urgently transported. He probably had no electrical activity by the time paramedics evaluated, also (aysytole-- which in chest trauma is more a confirmation of death than a "rhythm" disturbance to be treated.) Aystole in the field from a GSW at close range to the chest is not survivable.
Powder burns and stippling:
This link contains pics of GSW in clothing worn by victims who have been shot.
http://www.firearmsid.com/A_distanceGSR.htm
*Warning- this source contains links to autopsy pics of GSWs, which may be unsettling to some. The text contains no actual pictures.
http://library.med.utah.edu/WebPath/TUTORIAL/GUNS/GUNINJ.html
(For the mods-- I am new to WS, and I have submitted my credentials as a health care professional for verification.)