Three men have been arrested on suspicion of carrying out five arson attacks in Kent.
Five firms, within an eight-mile radius of each other in the Maidstone area, have been set alight since October.
No-one has been injured in the attacks which included the offices of MP Hugh Robertson in Lenham.
Kent Police said a 19-year-old-man, a man aged 22 and a 34-year-old man had been arrested on suspicion of arson on Thursday.
Each of the buildings had been daubed with a yellow painted number in a circle to signify the order of the attacks.
Threats to police
The first was on 28 October, when a blaze damaged a shop and the offices of MP Hugh Robertson in Lenham.
The most recent fire was on 30 January, when a garage in Headcorn was targeted and the number five daubed on the building.
The three other arson attacks were at a garage in Boughton Monchelsea on 29 December; Warmlake on 28 January, when a bathroom and kitchen showroom was targeted, and on 29 January at a garage in Ulcombe.
The hunt for the people responsible for the attacks were stepped up after threats were made to a police officer via an e-mail to the Kent Messenger newspaper.
Ch Supt Matthew Nix said: "Although this investigation is ongoing and still in its early stages, I would like to thank the Kent Messenger Maidstone for their continued assistance with this case.
"Their community spirited actions are a shining example of police and public working together."