Journalist starts to gather evidence on Sweden's borders (5)
I believe the answer is:
edges
'borders' is the definition.
(an edge is a border or margin)
'journalist starts to gather evidence on sweden's' is the wordplay.
'journalist' becomes 'ed' (short for editor).
'starts to' says to take the initial letters.
'on' says to put letters next to each other.
'sweden' becomes 's'.
The first letters of 'gather evidence' is 'ge'.
'ed'+'ge'+'s'='EDGES'
(Other definitions for edges that I've seen before include "Boundaries of a surface" , "Slowly moves" , "Outside limits" , "They're farthest from the middle" , "Sharpened sides of knives etc" .)