Munitions from World War One and World War Two were found at a house in Newport Pagnell last week, the third property to be raided by police.
A 37-year-old man was arrested on suspicion of stealing from heritage and protected sites after the munitions were found on Friday.
A house in Windmill Avenue was raided on Wednesday and a house in Bicester, Oxfordshire, on Thursday.
Detective Sergeant Pete Frost from Hertfordshire Constabulary said: “I can confirm that the Thames Valley incidents are linked to our investigation and the warrant that was executed on Wednesday September 17 in St Albans.
“Our investigation is on-going and we will continue to liaise with Thames Valley Police and partners in English Heritage.”
The arrested man is due to answer bail on November 11.
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