The case involved allegations that a man had coerced his 14-year-old stepdaughter to have sex with him. It was also alleged that prior to intercourse he provided her with a contraceptive commercial product called Encare, which is a vaginal insert that provides both a physical barrier and spermicidal action. After examinations of some victim vaginal swabs had proven negative for seminal fluid or any other sources of the suspect's DNA, the authors were asked to identify traces of the Encare product on the remaining victim swabs as well as two penile swabs from the suspect; the victim claimed the accused had not worn a condom. This paper's description of the materials and methods used in the testing procedure encompasses the chemicals, biological sample protocol, the preparation of samples for mass spectrometry, and the use of mass spectrometry. DIOS is a new sample ionization technique for laser desorption-ionization mass spectrometry. It has proven to be a sensitive and effective method for identifying traces of those molecular species that cannot be separated and identified by gas chromatography/mass spectrometry, but are in a mass range of a few hundred to a few thousand Daltons. In the current case, this procedure clearly distinguished the spermicides nonoxynol-9 and octoxynol-9, as well as different molecular weight ranges of polyethylene glycol. At trial the defendant's attorneys stipulated that their client had added some Encare to SLIP Plus (a commercial sexual lubricant that also contains nonoxynol-9), a sample of which was provided to the authors by the suspect's attorneys. 8 figures and 8 references