Several Ford Transit vans have been targeted by thieves for power tools.
There were eight offences between 7pm on May 23 and Tuesday 24 in Borehamwood.
Police are appealing for anyone with information to contact them.
Hertsmere detective inspector Matt Phillips said: "Offenders are deliberately targeting vans for power tools with seven of them being Ford Transit vans and recently they have been in the Hillside area of Borehamwood.
"Most have had their locks popped. We hope the public will help us identify the people responsible.
"We believe three men dressed in black are involved. Any further descriptions of the men would be useful to our investigation.
"I would like to reassure van drivers that we are fully investigating these incidents and have Operation Cruse running which involves high-visibility patrols."
Anyone with information should contact Hertfordshire Constabulary on 101.
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