This is the Case XX Lockback, has Stag handles and Brass liners.  The blade steel is 440C and finish is Polished.

Maker : Case XX
Handles : Stag
Pattern : Lockback
Model : DE151504L
Factory ID : 02986
Condition : New/Mint
Year Produced : 2002
Lock Type : Lockback
Blade Steel : 440C
Liners : Brass
Bolsters : Nickel Silver
# Blades : 1
# Backsprings : 1
Closed Length : 3 inches
Half Stops : No
Factory Box : No
Blade Finish : Polished
Country : Germany
Notes: : Very rare Boker made Case XX

In the early 2000's Case contracted with Boker to make several lockback and fixed blade patterns for them.  Great knives, but they didn't go over very well with Case fans - so it was cancelled after only one year.