I fail to see why it being prepared to be towed is extremely suspicious, at least in the sense of foul play although I'm sure that will be thoroughly investigated. Don't know anything about the 787, but if they were prepping to tow, it seems like a least some of the systems were powered up. Aren't the brakes electric? If so and they had someone preparing to be a brake rider in the cockpit wouldn't some sort of electric power have to be on for the brakes to be operated?