Thinking on what has been written here, if indeed it was MS's gun that DM apparently had possession of, AFTER the murder (which to me, doesn't make sense for him to have it in the first place if it belonged to MS and MS was the murderer), then it doesn't make sense for DM NOT to want it to go back to MS. What incompetent person would take the risk personally of taking someone else's murder weapon, when that someone else had killed a man during his presence, and give it to yet a different friend who had nothing to do with it, and expect THAT friend would remain silent... knowing that if that friend talked to police, it would all be looking like DM's murder weapon? Why would someone/anyone who didn't own or use the gun, take that kind of risk with an item that had nothing to do with himself, and everything to do with the 'real killer'?
On the other hand, if it were DM's gun, and DM was the trigger-man, and DM therefore had the gun afterward (and why wouldn't the shooter still be in possession of the murder weapon? Who is going to kill a man and then just nonchalantly allow the murder weapon to get out of his control and into someone else's control who could potentially hold it against him later?), as well as beforehand, which would make much more sense, why would DM want his associate, who was physically present and the only living person aside from himself who could give eye witness testimony as to the activities that night, to have possession of it?
He wouldn't, for the obvious reason that in case MS betrayed his trust and went to the police with everything he knew, along WITH the evidence of DM's gun (whether or not it still had DM's prints on it). So what does DM do? Stupidly, he brings some innocent friend into the picture and takes the gun to the friend's parents' house, instead of pitching it in Lake Ontario, or whatever. And on top of that, he doesn't answer his friend's 'joke' when he asks if the toolbox contains guns. And on top of that, he doesn't tell his friend that he doesn't want his partner in crime to get ahold of this toolbox. I guess it might help to potentially explain his thinking if we remember that DM thought he had covered all of his bases and that there would never be enough evidence to substantiate murder charges against him.
All moo