Massachusetts Attorney General Tom Reilly said Tuesday he is treating the concrete collapse in a Big Dig tunnel that killed a motorist as a crime scene that could lead to charges of negligent homicide.

Reilly's office already has begun issuing subpoenas to those involved in the design, manufacturing, testing, construction and oversight of the panels and tunnel.

"What we are looking at is anyone who had anything to do with what happened last night," Reilly said. "No one is going to be spared."

Gov. Mitt Romney said Tuesday he is taking legal action to oust the head of the Massachusetts Turnpike Authority after a woman was crushed to death by falling cement in a Boston Big Dig tunnel.

"People should not have to drive through the Turnpike tunnels with their fingers crossed," Romney said. "Neither I nor anyone else could be or should be satisfied until we have new leadership at the Turnpike authority."

At least 12 tons of concrete fell from the ceiling of a connector tunnel late Monday. The driver of the crushed car managed to crawl through a window to safety, but his wife died when four of massive concrete ceiling panels fell on the vehicle.

The debris and danger shut down the Interstate 90 connector tunnel they were driving through, backing up traffic for miles during the Tuesday morning commute. Authorities hoped to reopen it Wednesday, but they were still removing about 30 ceiling slabs from the accident site and checking at least 17 other areas with similar "tiebacks" holding ceiling panels in place.

Massachusetts Turnpike Authority Chairman Matthew Amorello said a steel "tieback" that had held a 40-foot section of ceiling over eastbound Interstate 90 gave way, letting the concrete slabs loose as the car drove beneath them.

"There was a snapping sound heard," Amorello said. "One of the tile panels from the roof released. It caused a series of panels to be released."

The accident was near the entrance to the Ted Williams Tunnel, which runs under Boston Harbor to Logan International Airport. Amorello said he had ordered a precautionary inspection of that tunnel as well because it has similar tiebacks, though a different ceiling structure. He said similar tiebacks were also used in 17 spots on the Interstate 90 section of the Big Dig and all were being checked.

"We feel awful about what happened last night," Amorello said. "It's an awful, awful tragedy. ... This is an awful situation that occurred."

He appointed a state police major, two outside consultants and a team from the Federal Highway Administration to assist in the investigation.