T/C Blower elbow explosion

Recently on one of our Tugs, which has Caterpillar 4 stroke Engine 3608, there was an explosion from Turbocharger (blower side) outlet elbow just before air cooler.
We found some lub oil in air cooler & intake manifold but we found some oil in other Engine’s manifold as well (it has two engines).
Just after the elbow (before air cooler) there’s a emergency shut down valve.

I can’t figure out what caused the explosion?
A) Was it the emergency shut down shut accidently, which causes rise in pressure?
B) Was it oil & some source of heat travelled through inlet valve all the way from inlet manifold, aircooler to the elbow?
C) Any thing else we are missing?
Please let me know if you need any photos or any other information.

Could you please help in figuring out the cause of accident.
I would highly appreciate it.
Thanks & regards,