Photoemission features associated with states deep in the band gap of n-SrTiO3(001) are found to be ubiquitous in bulk crystals and epitaxial films. These features are present even when there is little signal near the Fermi level. Analysis reveals that these states are deep-level traps associated with defects. The commonly investigated defects - O vacancies, Sr vacancies, and aliovalent impurity cations on the Ti sites - cannot account for these features. Rather, ab initio modeling points to these states resulting from interstitial oxygen and its interaction with donor electrons.