Period returning interrogators had to eliminate (9)
I believe the answer is:
eradicate
'eliminate' is the definition.
(synonyms)
'period returning interrogators had' is the wordplay.
'period' becomes 'era' (era is a kind of period).
'returning interrogators' becomes 'dic' (I can't justify this - if you can you should give a lot more credence to this answer).
'had' becomes 'ate' (e.g. I had an ice cream).
'era'+'dic'+'ate'='ERADICATE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for eradicate that I've seen before include "scratch" , "Dispose of" , "Exterminate, extinguish" , "Get rid of, remove all traces" , "Stamp out, remove all traces of" .)