The detective testifies that on Dr. Olson's latex gloves, traces of oils of Dr. Olson's skin flakes were found on the inside, and on the outside both skin secretions from the victim, and grape jelly. It is later revealed that Dr. Olson gratified himself in his office and on return he found the victim in his dentist chair with the jelly in her throat. Now, he either put on gloves before trying to resuscitate her (which is odd), or he gratified himself still wearing the gloves that he used when he cleaned the victim's teeth - in which case, surely, there would at least be some traces of his skin on the outside of (one of) the gloves.