LEF, short for logical evidence file, is a proprietary format created by EnCase Forensics software. It keeps record of evidences in a file having extension L01. Besides, users can select required evidences from a disk image (for instance, E01 file format) and save them in LEF L01 file extension.

More on EnCase LEF File Extension

LEF L01 file format helps investigators to keep track of digital evidences.
L01 files are mainly used to extract & store selected evidences from an entire disk image.
Unlike E01 which is a replica copy of an entire disk, L01 extension saves only necessary data
EnCase LEF holds all files and folders in their original format.
All meta properties including file name & extension, file size, created date, modified date, permissions etc are kept intact.
EnCase LEF format uses MD5 hashing algorithm to verify data integrity.