I'm sorry, but I agree with this, and it is the sort of protection you would invoke over your private life in a SIMILAR circumstance.
The family has a right to keep the photos private, unless there is probable cause a crime has been committed, then they could be seized under the 4th amendment. Apparently, no judge anywhere has yet thought there was sufficient evidence of a crime to invade the family's right to property.
This is called "a fishing expedition".
Did you read the transcript? If you did, then you'd know that's the legal issue to be decided. Favish argues that so far, the courts have not granted survivors the right to privacy on behalf of a dead crime victim. IOW, Foster's family doesn't get the right to keep Foster's crime scene photos private.
The reason the FOIA was passed was, in part, to protect the public against government cover-ups. This case has all the earmarks of a cover-up, and needs sunshine.
Even so, I think the USSC will rule against Favish. I hope I'm wrong.