  We coincidently measure the molecular frame photoelectron angular
distribution and the ion sum-momentum distribution of single and double
ionization of CO molecules by using circularly and elliptically polarized
femtosecond laser pulses, respectively. The orientation dependent ionization
rates for various kinetic energy releases allow us to individually identify the
ionizations of multiple orbitals, ranging from the highest occupied to the next
two lower-lying molecular orbitals for various channels observed in our
experiments. Not only the emission of a single electron, but also the
sequential tunneling dynamics of two electrons from multiple orbitals are
traced step by step. Our results confirm that the shape of the ionizing
orbitals determine the strong laser field tunneling ionization in the CO
molecule, whereas the linear Stark effect plays a minor role.
