Regarding the headphones, I believe page 2 of Investigator Chris Serino's report says that the headphones were initially found near Martin's body: "… a bag of Skittles candy, a red 7-11 red lighter in his pockets, headphones next to him, and a photo pin on his sweatshirt."
There are some inconsistencies, but we know the pin was removed during CPR and placed in Martin's pocket during transport to the morgue. The earbuds may have been placed in his pocket in the same manner. Or Serino's report may not have been correct.
“but we know the pin was removed during CPR and placed in Martin’s pocket during transport to the morgue”
That is not known.