Long time lurker...sometime poster here.
Just curious, what makes you think it's a temporary plate? Even though I've heard law enforcement is holding back info, I imagine they would have released it if LE had a plate number.
Then again, they probably already have some info on the white Elantra's driver from the surveillance footage, like their race, physical features, etc.
Likewise, I imagine they are combing through white Elantra DMV info and comparing their owners against known criminal and sexual offenders.