Investigators probing the cause of a house explosion that killed two young sisters have released a long-awaited report suggesting the building's natural gas system was not behind the deadly blast.

But an attorney representing the parents of the two girls yesterday dismissed the report's findings, calling the tests fabricated and suggesting key evidence has been overlooked.

"After one year, we have a report that tells us nothing, other than under these artificial conditions we have a part that didn't come apart," attorney John Wozniak said. "Nothing contained in the report surprised us in the least."

The report, released last week, marked the culmination of more than a year of waiting to find out what happened July 24, 2002, when an explosion ripped through a three-apartment building in downtown Hopkinton.

The blast leveled the building, and trapped Tara and Heath Carey and the couple's two daughters, Violet, 5 1/2, and Iris, 4, in the rubble.

Rescue workers quickly pulled Tara and Heath Carey from the rubble, but the two girls did not survive.

In a quest to determine what led to the tragedy, investigators for the state later pulled pipes, fittings, and meters from the wreckage, and focused on a "transition fitting," a pipe fitting that connects the gas line from the street to the building's gas system.

After months of testing, though, officials released a report that leaves nearly as many questions as answers, Wozniak said.

Written by West Boylston-based Massachusetts Materials Research Inc., the report says testing showed the fitting was not the cause of the deadly gas leak.

"This testing indicates that the recovered transition fitting could not come apart...to cause leakage," the report concludes. "This indicates that the fitting came apart as a result of either 1) the explosion and/or subsequent collapse of the house located at 65 Main Street...or 2) the application of an unknown external force or forces prior to the event."

Wozniak seemed openly frustrated with the vaguely worded conclusion.

"That fails to take into account the multiple meter changes," he said. "(The fitting) may have been pulled or moved. It could have been a service call."

The meters that measure the gas use of apartment appliances were replaced in May, NStar spokesman Michael Monahan said a year ago.

But NStar did not confirm at the time allegations made by the Carey family and upstairs neighbor Tony Defreitas that bills received after the meter change more than doubled.

Wozniak also said yesterday that one apartment occupant has said she heard a sound like a jet engine just before the explosion, and described the noise as coming from an area where the meters were. Wozniak did not name the source.

The Mendon attorney yesterday also reiterated his complaints with how the tests were conducted.

Following the blast, the Carey family several times went to court, asking a judge to force the state and MMR to include them in the testing process. The family dropped their opposition to the tests after months of delays.

Wozniak yesterday also claimed MMR workers were forced to heat and freeze some parts and use glue to reconstruct the fitting, essentially creating an "artificial" test.

"I've said it from the very beginning, they went ahead and conducted this testing with a cloak of secrecy, without any input from any party," he said.

With the report finally complete, officials from the state Department of Telecommunications and Energy will use the information to develop their own conclusions about what caused the accident.

That report should be complete in about a month, DTE Executive Director Timothy Shevlin said. He declined further comment.

"This is still a pending matter," he said. "As is our long-standing practice, we don't comment on a pending investigation."

In the meantime, the family and Wozniak are preparing their case in a wrongful death suit.

Within months of the blast, the family sued NStar gas, their landlord and Holden-based pipe fitting manufacturer Inner-Tite Corp., claiming a faulty fitting was behind the explosion.

A similar case yesterday was settled for a record amount.

In that case, the widows of two Attleboro municipal workers sued after the men were killed when they punctured a natural gas pipe that had been labeled as safe.

In a settlement released yesterday, Bay State Gas Co. and a subcontractor, Central Locating Service LTD, agreed to pay the two families a total of $20 million.

Wozniak, however, was uncertain yesterday if the settlement would bode well for the Carey's case.

Where the Attleboro case had a clear chain of culpability, the waters are murkier in the Hopkinton case, he said.

"We've got a case where the testing and investigation has been going on in excess of one year, and there's still no conclusive results of what went on," he said.

For the family, he said, the case is not about winning a financial award, but getting the answer they have waited for.

"I'm not really interested in the monetary aspect of this," he said. "My clients are more interested in what occurred. They want to spare any other families in the commonwealth a similar pain that they've experienced and gone through.