There are plenty of cases where murder suspects claim they sold a gun, traded it off, or had it stolen while being investigated by law enforcement.
It does nothing to help their case and they are still prime suspects. A simple BOS could be thrown together real quick and it wouldn't be anything for a murder suspect to do to try avoid charges. This is why I make it clear in emails and text messages what the intent of the transaction is. Because if you cant PROVE that chain of custody, then you can certainly take the fall for it.
Had they been in closer proximity, then M2 could have been a prime suspect in the case. "I sold it to some guy with a DL in a parking lot" is what almost every detective hears and it will not get you out of anything.