State investigators conducting a criminal probe into the Big Dig tunnel ceiling collapse have reconstructed concrete panels that fell and crushed a car, killing a motorist.

Investigators from Attorney General Tom Reilly's office are focusing on how the panels were designed and whether they were properly secured and tested. Reilly is considering whether involuntary manslaughter charges are warranted.

Bolts, epoxy glue, anchors, concrete and other materials have been retrieved from the 120-foot area in the Interstate 90 Connector Tunnel where the accident happened July 10, and are being stored and catalogued at a facility offsite, said Reilly spokesman David Guarino.

At a State Police facility, another team has reconstructed the ceiling panels that fell and killed 39-year-old Milena Del Valle as she was driving with her husband to Logan International Airport.

Del Valle was buried Wednesday in her native Costa Rica.

"It's much like investigating a plane crash scene. You gather the materials, reconstruct and examine," Guarino said.

Reilly's office is also sifting through documents including memos, engineer field reports and contracts obtained by request and subpoena from the designer, the contractor, and the project manager.

After the accident, Gov. Mitt Romney took over supervision of the repairs and the decision to reopen the two tunnels that were closed for safety reasons. But several federal agencies, as well as Reilly's office, have launched their own investigations into what happened and whether there were advance warnings of a possible ceiling collapse.

Most of the investigations are looking at the epoxy glue used to secure the ceiling panels and their design, as well as whether there were timely inspections, federal and state officials said.

Romney has declared all the bolts that use epoxy glue in that tunnel to be unreliable and they're being reinforced with either a steel-to-steel connector or anchor bolts. He has also called for full disclosure of when inspections took place and has questioned whether there were enough inspections.

The Big Dig project, the most expensive in U.S. history, buried much of the city's highway network in tunnels. It took over a decade starting in the early 1990s to complete and has since been plagued by leaks, falling debris, cost overruns, delays and problems linked to faulty construction.

Meanwhile, engineers and construction workers Wednesday worked on ways to reinforce all the ceiling panels in the tunnel where Del Valle was killed. Romney wants the tunnel opened as early as next week.