The frown was because he'd realised his plan had been rumbled... and grin appeared when the cameraman shouted - "SAY CHEESE!"
Cue Holly - "You can't tell anything from a person's expression!"
That's not strictly true, if it was we wouldn't have body language experts, but I don't think it's possible to determine the underlying emotions without understanding the circumstances/stimuli. In the case of the JB clip above he was actually smiling at his friends and supporters who stood outside court to show their support:
http://www.theguardian.com/uk/video/2011/jan/30/jeremy-bamber-new-evidence-video@ 11.20 in
I'm sure we can all picture images of notorious criminals driven in and out of court in secure vehicles with a baying public and a handful breaking police barriers to bang on the vehicle. Where was the baying crowd when JB appeared at court?
I thought lessons might have been learned after Christopher Jefferies/Joanna Yeates but sadly not

I can appreciate others not sharing my views on JB's case based on the main aspects eg phone calls, JM's testimony, silencer etc, etc but an attempt to draw something meaningful from the above is imo nothing other than a modern day witch hunt and the sort of low level debate I have come to expect from the Blue Forum.
I suspect many would like to put me on witches chair over my support for JB
PS Myster is it poss to add times to non YouTube links?