jessica mejia , 20 , died when her drunk ex-boyfriend smashed their car into a pole in cook county , illinois in december 2009 .
sheriff 's deputies improperly undressed the young woman 's body at the scene and took photographs of her , according to her mother 's lawsuit .
but the sheriff 's office says it was necessary to take the photographs in order to preserve evidence that ultimately put the ex-boyfriend behind bars .
the case goes to trial next week .