Used to express the limited scope or extent of one’s information:she could be dead for all I know...
But for all Dirk knows, you could be out gallivanting.
In the refrigerator all she finds are some dried apples and celery and assorted condiments that could have been there since her last visit for all Sandra knows.
No-one asked her any questions, no-one searched her. She could have been a heroin mule or a gun smuggler for all anyone knew.