We postulate a Gaussian three-body potential among c~ particles and adjust its parameters so that, when it is added to the Ali-Bodmer c~-~ potential, a good fit to experimental energies of low-lying 0 + and 2 + states of 12C is achieved. With these potentials we made a linear variational calculation in a basis of harmonic oscillator functions which are translationally invariant, completely symmetric, and have a definite orbital angular momentum. We study the influence of this three-body potential on elastic and inelastic form factors, transition widths, Coulomb energy and charge radius of the 3-~ system. The 3-c~ potential improved results found with the Ali-Bodmer potential alone. We find the 0 + state to be a (non-rigid) linear chain and the ground state to be a triangle of c~ particles.