That's a lot of planning, and effort though. Essentially you're saying this villain, which would realistically need to be a team effort, would need to subdue, or more realistically kill every depot worker at the same time so that no calls for help to local authorities can go out. Now maybe the 4 tied up people ARE depot workers. That would be plausible if he only subdued them.

Then, once there is no opposition to hinder his plans to modify the trains brake lines, you would have to know ahead of time which model this trolley is. A lot of newer models have a feature where the brakeline is technically always active, just not engaged. Once you clip the brakes, it would snap shut. So right off the bat, you need to make sure it's an older model. Which, would be older then about 20 years old. I know that sounds like you wouldn't find any that old, but you'd be surprised. 20 year old rail system is actually very modern. In Cleveland we use a light rail system. It's not a true trolley, but it's similar. The ones on our tracks were first made operational in the 1960s. BUT! Ours are based on electricity which hang from a power supply line that runs above the track. So if you were to cut that, yes you'd cut the brake, but you'd also cut the ability to drive. And since our depot yard isn't near any hills, you'd just sit there.

Essentially what you're suggesting at that point, is a terrorist attack, which even if you did the months/years of planning to make everything carry out in oceans 11 style heist, you're still talking about killing 10-40 people to set up a situation where the sole purpose is to endanger either 1 or 3 peoples lives. All just to make one person feel guilty for "killing".

And I'm not even going to ATTEMPT to go into how even after all that, the psychological "victim" may not even give a shit, so the whole thing was for nothing.