  We show that dislocations should be the main source of spin tunneling in
Mn-12 crystals. Long-range strains caused by dislocations produce broad
distribution of relaxation times that has been seen in many experiments. When
the external magnetic field is applied along the c-axis of the crystal, local
rotations of the magnetic anisotropy axis due to dislocations result in the
effective local transverse magnetic field that unfreezes odd tunneling
resonances. Scaling law is derived that provides universal description of spin
tunneling for all resonances.
