Double ionization of the helium atom by slow electron impact ($E_0=106\mathrm{eV}$) is studied in a kinematically complete experiment. Because of a low excess energy $E_{\mathrm{exc}}=27\mathrm{eV}$ above the double ionization threshold, a strongly correlated three-electron continuum is realized. This is demonstrated by measuring and calculating the fully differential cross sections for equal energy sharing of the final-state electrons. While the electron emission is dominated by a strong Coulomb repulsion, also signatures of more complex dynamics of the full four-body system are identified.

• Received 16 August 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.193201