A detective is investigating a series of grisly murders in New York. The bodies of the victims seem to have been ripped apart by a inhumanly strong person. He has narrowed down the list of suspects to one individual, Henry Jekyll, a scientist working out of a lab in Queens.
He secretly follows Jekyll in order to gather evidence against him. On one night, he sees Jekyll drink some concoction taken from his coat, which turns him into a freakishly large man, and kill a prostitute. He collects DNA samples of the man (blood, hair, fingerprints), but results don't provide a match for Jekyll. The detective obtains a warrant to search the doctor's premises, locating a diary describing his actions as of late. The journals detail the doctor's experiments of how he invented a concoction that allows him to bring his darker nature to the surface, allowing him to indulge in his vices without guilt or fear of discovery.
If the doctor and this other person are the same, how can it be that they don't share the same DNA?