Alright, hello Moviepilot, this is my first theory.
I know it is pretty shocking that Barry Allen whose main intention is to save his mother IS THE KILLER OF NORA ALLEN!!
Now, before you read this theory you should know the storyline of the Flashpoint Paradox. And, also before making fun of this theory, theories are meant to be lame guys. Nobody makes fun of the String Theory, do they?
Alright, this theory is a little rough, and lots of things are unexplained, so other theor-ists may help me.
Now, this theory starts with Barry again trying to save his mother. He runs and runs and creates a time warp or Worm hole or whatever it's called then while in the 'Time Warp' he sees the Reverse Flash running towards him. Then Barry either gets distracted or punched or something like that and hence, accidentally creates the Time Boom or The Flashpoint Paradox.
Then, the Flashpoint script starts
He finds out he saved his mother, lost his powers, Thomas became Batman, Martha became Joker, there is WW3 and so and so and NOT TO FORGET that he has the Yellow suit in the Flashpoint Dimension because this plays a key feature in this theory.
Let's skip to the end....
So in the end, the world is going destroy because of Aquaman's orders and Barry beats Zoom then again opens that 'Time Warp' and then we come back again to start of the theory where Barry of Past tries to save his mother. But remember, I told that Barry of the Past sees Reverse Flash. But actually that is not reverse flash but Barry of the Present. Remember he wears Reverse Flash/Zoom's suit in the Flashpoint Dimension. But Barry of Past mistakes him for Reverse Flash/Zoom. Then Barry of the Present tries to stop his Past to save Nora. Then Red Barry (Past) creates the Flashpoint Paradox. Whereas Yellow Barry(Present) goes out of the 'Time Warp' and goes to the Past(Accidently) where Nora's murder is going to take place. Then his hand some how gets the murder weapon. Maybe, he picked it up or it was a result of a time paradox. Then he stabs Nora with that. Maybe, because he told everything to Nora and she forced Barry to stab her or maybe because he realised that saving Nora may result in Central City with no Flash or maybe something worse.
Now lots of things are unexplainable
So here is where the theor-ists may help me. Small Barry claimed that he saw Two speedsters but that may be explained, Maybe, Barry Past fought Barry Present before creating that 'Time Portal'. The other thing is that Why would Eobard Thawne claim that he killed Nora Allen. Maybe, Barry Present disguises himself as Dr.Wells to guide the other Barry. I know all of this is rough that is why I request the other theorists to help me.