Roland Perry wrote:
In message , at 16:54:53 on Sun, 17 Sep
2017, Graeme Wall remarked
did they pick him up because they had managed to get a name/face for the
person they were looking for

or did he give himself away

Look at Train CCTV of man with with bag getting on at station xxx
look at CCTV at station xxx for the time period you expect someone on
that train to have entered the station and see same man with same bag
touching in.
Strike lucky and find he used a registered Oyster card.

Or he's a minor criminal with a record and fingerprints/DNA on file.
Get a match from the bucket.

Very little hard information two days later. One arrest in Dover,
another in London; are either firmly linked to forensics from CCTV and
the bucket, or because of something else?

Presumably information will remain limited if they're still looking for
more suspects, suppliers, funders, inspirers, etc.