They've known since very shortly after the murders that someone use the victim's ATM card. There are no bank records which can show the identity of an unauthorized person who used a card. The security videos can be helpful, but they're often blurry, and if you cover your face the ATM still works, so there may not be any face visible in the video. Even if there is, you then have to figure out who the face belongs to -- most people don't have their names printed on their foreheads.
"most people don't have their names printed on their foreheads"
NOOOOOOO! Who told you that lie ..??
Last article posted about this said they finally had a license plate number from the cameras.