BOSTON -- An outside engineering consultant spoke out Friday about the inspections into the Big Dig tunnels.

NewsCenter 5's David Boeri reported that officials were trying to determine why a 3-ton section of the ceiling in the Interstate 90 connector tunnel fell Monday night, killing Milena Del Valle, 38, of Jamaica Plain.

"In any project, you have three things that are pulling you. One is the schedule, the second is the cost and the third is the quality, and these tend to pull in different directions," engineering consultant John Christian said.

Christian said that the earlier problems with the Big Dig -- including leaks in the tunnel and problems with the slurry walls -- did not compare to the current problems.

"That was bad, but even at its worst, I don't think it posed a threat to life and limb," Christian said.

Christian applauded the approach to inspecting the tunnel's panels and bolts.

"They have been, in my opinion, very conservative about this. For example, they basically said that if there is as much as one-sixteenth of an inch of relative displacement between the plate and the concrete to which it is supposed to be bolted, that's one that goes on the list to be looked at further," he said.

Meanwhile, suspect bolts and fallen panels are being held by police as evidence for a criminal case as detectives search construction records.

"What we are going to try to do is put our physical evidence together with the document evidence, and we are going to try to come to some conclusions here. We are making every effort to hold whoever is responsible for what happened accountable," Attorney General Tom Reilly said.

Christian said that he doesn't expect the tunnel to open soon.

"A lot of people are going to have to be satisfied before they can decide what to do to repair things and when they can open the tunnel. I am a little reluctant to make any predictions about when that is going to happen," Christian said.