^^BBM
From the AA, following up on info obtained from MW's host, detectives identified CS and traveled to the address obtained from his DL on the morning of 5/12 (the murder occurred on the evening of 5/11).
At that time, CS agreed to come to the APD homicide office to speak to detectives. CS was advised he was free to leave at any time. There was no probable cause to detain/search CS at this date/time including testing for gunshot residue.
(It further appears it was not until after 8 PM that authorities obtained a signed search warrant to secure CS DNA. I suspect ballistics from the spent shells from the crime scene and/or the victim's body were not yet matched to the weapon purchased by CS for AS).
According to Wikipedia, gunshot residue only lasts about 4-6 hours.
Gunshot residue is the consistency of flour and typically only stays on the hands of a living person for 4–6 hours. Wiping the hands on anything, even putting them in and out of pockets can transfer gunshot residue off the hands.
Also on 5/12, while CS was talking to investigators at APD, an unrelated arrest warrant was served on KA at the residence she was sharing with CS, and she was transported to APD. At this time, she was briefly interviewed about her knowledge of MW's death, shown surveillance of her Jeep near the residence where MW was shot, and KA remained quiet.
When KA's unrelated arrest warrant was determined faulty, she was advised she could leave at any time (since there was no probable cause to neither detain nor search KA for gunshot residue, DNA, etc).
We know it was near the time KA was being interviewed that a search warrant was obtained and executed at the residential address of CS/KA where the guns CS described to detectives were located. It's unknown whether or not clothing was identified and collected during this search.
IMO, I don't think one can cite failing to test either CS/KA for gunshot residue when probable cause had not yet been met as a rookie mistake -- it's the law!
While it's possible gunshot residue tests were later taken from CS and not shared with the public,
I don't see the value in testing either subject for gunshot residue more than 24 hours after the incident, if only to deny the defense a negative residue test to glean on to and later use for at least 100 sound bites-- professing their client's innocence. MOO
en.wikipedia.org