A state law in effect since January may make it difficult for thieves to cash in on copper fittings and tubing stolen over the weekend from two Derouin Plumbing & Heating Inc. vans.

Gary L. Derouin, secretary and treasurer of the company at 139 Mill St., said the value of materials stolen sometime between Friday evening and Monday morning had still not been calculated Tuesday, but added it will exceed $1,000. Some tools also were stolen, he said, and their value exceeds $600.

One of the tools, a center-cut for sheet metal, had just been purchased and was used for the first time Friday.

Police said somebody climbed over a fence to reach the vans, which were parked behind the store and off Newell Street. One truck had been left unlocked, and the other was entered by smashing a window, police said.

Mr. Derouin suspected at least two people were involved, and said they apparently passed the stolen items under the gate.

If the thieves try to sell the copper, they will be required to provide their photo identification, according to a woman at Perkins Scrap Metal, 129 Factory St. The new law requires buyers to check ID for transactions exceeding $50 value, she said.

Mr. Derouin said his company will be better prepared the next time. A security system is being installed, he said.