No causes have been ruled out as the National Transportation Safety Board begins its investigation into the collision of two Metro-North trains, crippling rail service in Connecticut.

Investigators arrived around 9 a.m. Saturday, May 18, at the Fairfield-Bridgeport line, where one train derailed and was struck by another, headed in the opposite direction, around 6:10 p.m. Friday, May 17.

Gov. Dannell P. Malloy said the equipment has been ordered by the state Department of Transportation to remove the trains from the tracks, but it can’t be used yet as the on-scene investigation begins.

Malloy, local officials and NTSB investigators examined the tracks and train cars Saturday morning.

It was estimated Saturday that the on-scene investigation could take seven to 10 days, but the tracks will not need to be closed that long. However, Malloy said, there is still no determination yet when the tracks will be reopened and full service can be restored.

Two tracks near the scene of the crash were already out of service as crews work on the catenary system, which carries electrical wires to power the trains.

"People will have to be patient. We want to get this investigation right whether that takes one day or several days," U.S. Sen. Chris Murphy said at a Saturday press conference where he was joined by Sen. Richard Blumenthal and U.S. Rep. Jim Himes. All three men marveled at the damage caused when the eastbound train derailed and was struck by the westbound train.

"I feel we are fortunate that not more injuries were the result of this tragic and unfortunate accident" Blumenthal said, adding that he believed the new Metro-North M8 cars that were recently purchased may have played a part in preventing further injuries or worse.

"Investment in infrastructure and investment in quality of transportation is probably one of the lessons we will learn from this accident," he added.

Blumenthal said that he and Murphy had been assured by the NTSB they will finish "as quickly as possible at the scene" to clear the tracks and added, “I am very heartened and encouraged by their total dedication to getting Connecticut back to business.”

With no determination yet what caused the derailment, the speakers at Saturday’s press conference urged patience.

Blumenthal said while the best current speculation is focusing on tracks now,  "Nobody knows right now and no one should leap to conclusions about what the causes are. That’s why the NTSB is here."

The NTSB will be looking at braking performance for the trains, the conditions of the wheels and the cars and the track. Additionally, the NTSB will examine the signaling information to see if the signals were operating properly, as well as crew performance.

"In terms of human performance we will be looking for anything that would affect the operator's performance or behavior" the NTSB said Saturday.