Re: My first thought ...
"Breaking" stories are often missing information for all sorts of valid, non-conspiracy reasons. The initial reporting can also be very vague, confused and misleading. The media (plus unsocial media) will be clutching at anything to get a story.
It doesn't mean it is being "withheld".
I was working in central London on 7th July 2005 when the terrorist bombs went off (one destroying a bus in Tavistock Square and three in different location on the London Underground). The initial reports were mostly rumour and hearsay (not to mention frequently flat wrong) because it took time to work out what actually had happened and the priority was dealing with the incidents and the casualties and not giving "press briefings".
It was only quite a bit later that accurate information came into the public arena.
Even then, sometimes crucial information may be withheld, for very valid reasons, if releasing it could interfere with or otherwise prejudice the investigation.
As you say, it takes time to get video expertly analysed so releasing it before then could be very misleading until law enforcement have a clearer understanding of what it actually it shows.
Rushing to the press before establishing the facts often is NOT the best thing for law enforcement to do in an on going case.
Also, someone has to "edit" the video to release an edited version. Doing that properly also takes time so the released edit is not misleading.