The production of high-momentum electrons in double ionization of helium by near-infrared lasers is investigated using three-dimensional classical ensembles. The nucleus’ role is examined by systematically adjusting the nuclear potential. The primary source of the high-energy electrons is found to be backscattering off the nucleus at recollision. Recollision excitation with backscattering of the unbound electron is found to be especially important. It is shown that recollision excitation with ionization before the next field maximum can lead to a correlated electron pair.