Henry Williams is a resident of the Lenten Pool area of Denbigh, who heard the explosions caused by John Larsen, near to their homes earlier this year.
He said he thought it was somebody letting off fireworks, until one Sunday morning when "big damage" had been done to some cars - "and that's when I felt a bit worried."
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The force said they have received reports of incidents and are urging people to not give out any financial details.
Officers from Dyfed-Powys Police stopped the car that had travelled around 175 miles from London on Wednesday.
An ITV Wales poll shows support for lockdown and fears of Covid-19 risks on public transport, as well as from shopping and other activities.