lack oil pressure - dead engine? Please help

[ZaX]

Few days ago I was crusing in my ae86 on a highway.
5th gear, 140kmph, around 5000rpm.
I noticed that my oil pressure gauge was near the low sign. I started to slow down. As I slowed down, the oil pressure was falling lower and lower, until it stayed on 1/4 od the gauge, check engine light goes on.
As I stoped i heard strange mechanical noise from the engine. Also engine would not idle, just dies. It took 30 sec for me to slow down.
So I check the oil level, it's ok, enough coolant, no overheating, but dead engine.

I looked bit in to the radiator, looks like clear coolant, no oil, so headgasket looks OK.

Called the towing truck and towed AE86. I didin't want to drive it.

So, I asume
a) spun bearing on crankshaft
b) oil pump

What should I do/check first?
Can I remove the oil sump from the engine without taking the engine out?