Defense lawyers urged jurors to be cautious in evaluating DNA evidence linking their client, Jesse Matthew, to a brutal attack in 2005 on a woman in Fairfax.
Matthew's trial in the Fairfax case began Monday. He also is charged with the abduction and death last year of University of Virginia student Hannah Graham.
During opening statements, prosecutor Ray Morrogh said a struggle between Matthew and the victim produced the DNA evidence that links Matthew to the crime.
But public defender Robert Frank warned jurors that DNA sometimes is transferred from one person to another inadvertently.
Matthew is charged in Fairfax with attempted capital murder, abduction and sexual assault in connection with a 2005 attack on a woman walking home from the supermarket. He's pleaded not guilty.