Captain, your doctor is a hardened criminal, now disguised or altered to appear as a woman. He is wanted across human space for crimes committed in over two dozen star systems.
Captain, I've been a woman my whole life, and this stint with you is the first time i've left earth.
Hah! a likely story!
I can prove it with employment records, and hundreds of air-tight alibis.
Obviously you've murdered an attractive young woman, and assumed her identity in order to escape detection. Another crime to add to your docket!
Ahh... the long arm and short wit of the law.