Getting out of bed and leaving their new Milford apartment often takes too much effort.

But Tara and Heath say they get by, if only because they are consumed with a desire to find out why Iris and Violet died. The sisters were killed when an explosion destroyed their Hopkinton apartment building July 24.

Iris was 4 and Violet would have turned 6 in November.

"Violet and Iris had the rest of their lives to live and it was taken away from them and we want to know why," Tara Carey, 28, said through tears.

The answers have yet to come. The state fire marshal's office and the state Department of Telecommunications and Energy, or DTE, have only begun to investigate the deadly explosion. Testing on pipes, fittings and meters pulled from the Main Street apartment building began earlier this month at Massachusetts Materials Research Inc., or MMR, in West Boylston.

The Careys and their Mendon attorney, John Wozniak, have fought from the beginning to have equal participation in the investigation.

The Careys talked about their frustration yesterday in Wozniak's office. Their eyes were red, their voices cracked and their heads were bowed.

"We don't feel as though we're being fully included in the investigation," said Heath Carey, 27. "It just seems that they're not allowing us full access. We're there as spectators."

Wozniak will today ask a Middlesex Superior Court judge to grant the Careys full access to the investigation, including testing, meetings, photographs and documents. Wozniak worries valuable evidence will be destroyed or specific tests overlooked if the Careys don't have a say.

One test that concerns Wozniak and the Careys would be conducted on a broken pipe fitting taken from the basement of the apartment building. Experts at MMR plan to glue the broken pieces together and test the fitting for leaks, according to MMR documents.

"The proposed testing will forever alter the two surfaces that very well may be the cause of this horrific accident," Wozniak said.

The DTE has allowed victims to participate in investigations for the last five years, said its executive director, Tim Shevlin. That means victims have a chance to observe, ask questions and object.

"We would consider all comments, but we're still driving the bus on the investigation," he said.

Shevlin said department policy prohibits him from talking about the Hopkinton explosion investigation until after the matter has been decided in court.

On top of those worries, the Careys face the challenge of rebuilding their family. Heath Carey had a vasectomy in September 2001 as a form of birth control.

The procedure was reversed in October at MetroWest Medical Center in Framingham. The surgery was successful, but the couple has not been able to have children, Tara said. They are considering infertility treatments.

"It's very scary. It's very scary to know that we may never have children again. We want to try to have more children," said Tara, her eyes welling with tears.

"The way we are looking at it is we'd be bringing Violet's and Iris' sibling into our life -- who will be a part of them."

Tara and Heath have tried to get on with their lives as best as they can. They moved out of Tara's childhood home and into their own apartment in Milford this December. They go to therapy once a week. And they continue to operate their clothing business, freakandfrolic.com, from their apartment.

But the holidays went by with little celebration.

On Christmas Eve, Tara and Heath wrote Santa Claus a letter and asked him to watch over their daughters. They spent Christmas Day in their pajamas and ate macaroni and cheese for dinner. Their fifth wedding anniversary also went by on New Year's Eve without fanfare.

The closest they got to a celebration was on Nov. 29, the day that Violet would have turned 6. Heath and Tara brought balloons to the blast site and visited the girls' joint grave.

"Violet wanted to have her sixth birthday party at McDonald's with her friends," Tara said. "So we went to McDonald's and we got them Happy Meals and brought them down to their grave and left them there."

The couple's new apartment is filled with whatever photos and videos family and friends could copy for them. Most of their own mementos were lost in the explosion, including a paint impression of Violet's fingerprints and a video of the family's July 4th vacation on Cape Cod.

July 4th was the family's favorite holiday, the couple said. The girls loved the fireworks and being dressed up in red, white and blue.

Tara said she finds joy in replaying the family's last night together in her mind. July 24, 2002, ended as every other day did, with supper, a bath for the girls and hanging out in the living room with the television on as background noise.

"I do it because that's the closest memory I have of them," Tara said. "I'm able to hear their voices in my head and I'm able to see them."

But even those happy memories are hard to bear, Heath said.

"Any reminder of them that we have is a reminder that we don't have them," he said. "Any of the pictures we have or the videos we have, we watch and remember the times, but realize there won't be any more."