Tandem spectrometry (MS/MS) and collision-induced dissociation (CID) are used in forensic analysis. Correct precursor and fragment ion assignment is critical for accurate compound identification by MS/MS. Although mass spectra can be annotated with molecular formula using high-resolution m/z measurements, in many cases molecular structure remains unassigned for fragment ions generated by CID. For de novo molecular identification, in-silico generated MS/MS spectra are used as a reference. However, there is evidence that fragment ion structure annotations in these reference libraries are often incorrect. For that reason, we are investigating the fragmentation mechanism(s) of model compounds such as phenethylamine, the simplest species in the substituted phenethylamine class of drugs that include amphetamines and MDMA, to improve structure assignment. This presentation highlights how use of CID, ion (vibrational) spectroscopy and computational chemistry allows us to identify the pathways by which protonated phenethylamine eliminates neutral NH₃ and CH₂=CH₂ in sequential fragmentation steps.