How to recover files accidentally deleted from LUKS encrypted device?

I just "Permanently Deleted" two pictures from a folder in my disk that is encrypted with LUKS. I ran

testdisk

and navigated through the menus. It did identify the two now missing files but their entries indicated a size of zero. Is LUKS designed to wipe the empty space so that deleted files are not recoverable? Or was testdisk not fit for the job? Are there other tools that may help save my photos?