I actually do believe it possible that MS didn't ask for the toolbox knowing it had the murder weapon inside of it. Why would he have wanted DM's gun on him when he thought police may be coming for him next?
I believe MS had his own murder weapon to deal with and didn't want DM's as well. Perhaps once MS received the gun from DM via MH and AM, and MS knew that DM was in custody, MS worried that it was a signal that DM would try to pin the murder on MS. MS's concern about being blamed for everything by DM could indeed induce paranoia in MS. They acted together to murder TB but both later tried to say the other was solely responsible. That's how criminals behave - they can't be trusted to hold up their end of the bargain when the heat is on.
I also believe the Crown's story about how quickly the murder took place in the field. DM would have taken the risk to leave the Yukon unattended with the dog left inside, windows rolled down for air, but only for a short amount of time. I also believe MS and/or DM scoped out TB's area by mapping it ahead online, or physically driving in the area to find the perfect spot not only to park but to murder TB.
All MOO.
bbm - speculating, maybe some deal with Big Iisho, for instance DM had been asking him for a discount on the gun, maybe it was a pay-per-use deal and MS was to get it back to BI, thus the phone call.
as for scoping it out, would be easy making his way back from Waterloo via Brantford to 403 or Cambridge via hwy 8 enroute to Oakville & Etobicoke, but I think it could be why they were so late. Just scoped out a spot when they got there as MS suggested. I just don't know they are bright enough to be google mapping it, and LE might have had a record if they had. MOO