A system is disclosed for identifying a precursor ion of a product ion in a scanning DIA experiment. A precursor ion mass selection window is scanned across a precursor ion mass range of interest, producing a series of overlapping windows across the precursor ion mass range. Each overlapping window is fragmented and mass analyzed, producing a plurality of product ion spectra for the mass range. A product ion is selected from the spectra. Intensities for the selected product ion are retrieved for at least one scan across the mass range producing a trace of intensities versus precursor ion m/z. A matrix multiplication equation is created that describes how one or more precursor ions correspond to the trace for the selected product ion. The matrix multiplication equation is solved for one or more precursor ions corresponding to the selected product ion using a numerical method.