I/m sorry, but this sounds fishy as hell!!
1. Why was the driver driving through this area? If it is, as the OP stated, 'an area known for not being very safe', why the thunder did the driver drive past there and not take an alternative route that would not pass such an area? They could easily steal something off the flatbed at any stop-street, so you avoid such areas as a matter of logic.
2. A B&W DM70 'was promptly picked up by someone who literally ran off with it'??? Look at the size of that thing. Who was running away with it, Superman??? And why couldn't the driver chase the thief down? Is he/her an ancient geriatric with two bad knees?
3. The B&W DM70s 'apparently not secured properly by the driver'? This is also very suspect. These are clearly a high value items, so if you're in any way a responsible person, you'd make #%@ sure that thing is properly tied down!
Nope, I am sorry, but a proper investigation is needed here. If the driver is not someone who is well-known and trusted by the OP, I would strongly suggest investigating him/her. There are too many coincidences here.