Importance of semen evidence

Understand the importance of semen evidence.[1]  The relevance of semen evidence in cases involving male suspects covers the spectrum, depending upon case facts. Semen is composed of cellular and liquid components known as spermatozoa (sperm) and seminal fluid. Semen evidence can be useful because it is positive identification that ejaculation occurred,[2] and it can be used to positively identify suspects. However, it is critical to note that failure to recover semen is not an indication that a sexual assault did not occur. There are a number of reasons why semen might not be recovered in these cases: Assailants may have used condoms, ejaculated somewhere other than in an orifice or on patients’ clothes or bodies, or not ejaculated at all. Semen may have been depleted by frequent ejaculation prior to the sample in question.[3] Chronic alcohol or drug abuse, chemotherapy, cancer, infection (e.g., mumps or tuberculosis), or congenital abnormalities also may suppress semen production. Other factors may contribute to the absence of detectable amounts of semen evidence. For example, significant time delays between the assault and collection of evidence may cause loss of semen evidence, semen may be washed away prior to the exam or improperly collected, and an object other than a penis may have been used for penetration.

[1] Drawn from the West Virginia Protocol for Responding to Victims of Sexual Assault, 2002, pp. 31–32, and New Hampshire’s Sexual Assault: A Hospital Protocol for Forensic and Medical Examination, 1998, pp. 26–27.
[2] In the absence of sperm, certain seminal fluid components may be used to identify semen.
[3] If assailants who had a vasectomy ejaculated, their seminal fluid would not contain sperm.


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