First of all condolence for the departed and speedy recovery for the injured.

I would like to complete the narrative provided by member 1844918 (Saptarshi). I also base the assessment on Joint Investigation Report taken from click here Note: This based on available information and may change with new information.

Coming...
more...

to the facts:
1) 12841 (Coromandel) travelling at full speed (under green signal on main line) ends up taking a turnout (Junction Point #17) to the loop line, survives the turnout at high speed.
2) 12841 rams into stationary goods train rake. Loco and few coaches climb up on top of the goods train rake. Several coaches crumple up and many of them are capsized. Some of them fall on the DN main line where 12864 (SMVT HWH) was crossing.
3) Last two bogies of 12864 also get derailed on impact at high speed.

Possible points of failure :
- Mechanical malfunction at junction (without feedback to station master / cabin). I have not come across another instance of this happening, ever. Does anyone else know of such failures?
- Human error / sabotage of diverting 12841 to loop line : Unlikely, unless this was also accompanied by a signal failure .. as pointed out by members, signal won't be green when train is taken to loop line.
- I do not give much importance to classical RW theories of sabotage like fishplate damage, sleepers, etc. because those cannot result in 12841 loco climbing on top of stationary goods train. It can happen only if the rake rammed from behind in a controlled path (i.e. while on track).
- S&T works at junction point 17 are also not very plausible, because several trains would have passed this busy junction in the minutes leading to the accident. Besides, why would they be working at that hour?

It would be interesting to hear the accounts of a) crew from stationary rake, b) crew from 12864, c) guard of 12841, d) cabin controllers, and e) S&T staff working on #17, if any. Distances between different points will also help us understand exactly what happened .. for instance, how far was the guard's cabin of the stationary rake from the turnout. The story is not complete, but all indications are for a fault at the turnout (and not a human error), because it is the only plausible explanation remaining. As they say "If you eliminate the impossible, whatever remains, however improbable, must be the truth."

I welcome any criticism related to logical flaws in this story.

On a side note, imagine the horror if 12864 arrived a few seconds later.