Trigger AI character when certain condition is met

I am trying to trigger the AI character only when the player commits a mistake. So I have a bool variable which is initially false and I want the AI character to start chasing the player when the bool variable becomes true. But the problem is even though I declare it as public and static, somehow the the AICharacterControl.cs script doesn’t have access to the variable.
Second thing I tried is the Singleton example ( given here : Unity Connect ) but even that doesn’t work.
Can anyone give tips as to how I can have the boolean variable which is truly accessible at the AICharacterControl script so that I can trigger it? Thanks.

You can set and clear the Target Property of the AICharacterControl class.

When this property is null - the agent stops moving. When it is set, the agent will chase the target.

So, all you really need to do, is keep the target null in the beginning and set it when the player commits a mistake.