Trying to fix iphone 4 but not sure what is wrong

I was given an Iphone 4 from a friend at work to see what I could do.
She told me that it was dropped in water and she dried it out in rice.

Here are the symptoms:
1) It does not turn on
2) when I plug it into the charger, sometimes I will get two successive vibrationsindicating there might still be life in it.
3) the vibrations also occur occasionally after I take it off the charger and I am fiddling around with the phone
4) No lights at all
5) Tried booting to safe mode (hold the home and top bottom) nothing happens.

Now, I have taken out the screws and have the battery pack removed from the back, so I am able to disassemble this if needs be. How should I approach the rest of the repair?

 

Forgot to add, I haven't taken out the battery or any of the components yet and I have not put anything in Rice - the original owner said she did that.