Philosophy Kantian ethicsWatch
Kant's beliefs on theft are:
(Depends on the situation but) Theft takes away the autonomy of the victim.
Theft uses the victim as a means to the end of whatever is stolen (this goes against the Kingdom of Ends)
Theft is un-universalisable because you wouldn't like people stealing from you. If it was universalised, no one would be trustworthy.
There's more but I'm no expert.