BOSTON -- In Boston Thursday morning, the I-90 Connector remained closed after this week's tunnel ceiling collapse that killed a woman.

Officials were taking a close look at what allowed it to happen, and the problem may be worse than originally thought.

Newscenter 5's Steve Lacy reported that investigators continued to focus on the bolts that connected the ceiling panels to the tunnel roof. They identified 60 potential trouble spots in the eastbound connector alone and decided to expand their investigation into the entire highway system.

"Where there are bolts ... these individual locations where the threaded bolts were used, where something appears to have pulled out or be somewhat of a gap between the ceiling, those have been identified as potentially problematic. Those are being investigated further," Project director Mike Lewis said.

Investigated by state and federal officials who are trying to determine whether anyone knew of potential problems with the tunnel ceiling tiebacks that supported the 3-ton panels that fell Monday night, crushing the car Milena Del Valle, 38, was in. She was killed and her husband, Angel Del Valle, 46, escaped with minor injuries.

It now appears there were indications of problems dating back to 1999. How contractor Modern Continental and project manager Bechtel Parsons Brinkerhoff dealt with those problems is now a central question in the investigation.

"There were about five bolts that came out under testing and there was a plan to address this situation. We're trying to find out right now, was that plan implemented," Massachusetts Attorney General Tom Reilly said.

Concerns about whether potentially criminally negligent work may have been to blame for Monday's collapse has prompted state officials to take a closer look at the city's entire highway system. The probe will extend beyond the Big Dig to decades-old highway projects that were not part of the $14.6 billion Big Dig project.

In the meantime, Massachusetts Turnpike Authority Chairman was unable to offer a timetable for when the I-90 connector portion of the highway will be reopened.

"We had hoped to have things progressing more quickly but because of the nature of the crime investigation it's taking us more time than we would have anticipated," Amorello said.

An engineer who worked on the connector tunnel told The Boston Globe he had expressed concerns about the weight of the connector ceiling panels but backed off after he was assured by project officials that the panels were safe.