Its actually easier than you think. Most masks, scarves and balaclavas will have been purchased recently. Even if not, finding who has purchased specific ones will be easy. Most of these people will already be know to police, so will likely know the sizes of these people, down to shoesize...
<blockquote class="twitter-tweet"><p lang="en" dir="ltr">Just had this through <br><br>Intelligence is off the scale !<a href="https://twitter.com/hashtag/Rotherham?src=hash&ref_src=twsrc%5Etfw">#Rotherham</a> <a href="https://t.co/7xmBjOP79l">pic.twitter.com/7xmBjOP79l</a></p>&mdash...