BOSTON (AP) – The trolley operator who died in last month’s fatal Green Line crash wasn’t talking on her cell phone or sending text messages in the moments before her trolley slammed into a second trolley, authorities said Tuesday, deepening the mystery of what caused the accident.

There was no evidence that Terrese Edmonds was in communication with anyone on her cell phone – whether through phone calls, text messages or e-mail – immediately before the crash, Middlesex District Attorney Gerry Leone said.

The 24-year-old was killed and about a dozen passengers were hurt in the May 28 collision.

Leone also there also was no indication of alcohol or other drugs in Edmonds’ system.

Investigators from the National Transportation Safety Board have already ruled out a series of potential causes for the accident including problems with the track, the signals and the trolley’s brakes.

They also found nothing was blocking Edmonds’ view of a signal that would have required her to stop the train at the Waban station for 60 seconds and proceed at no more than 10 miles an hour.

Instead, the trolley was going 37 to 38 mph when it struck a train in front of it on the same track as the second train was pulling away at 3 to 4 miles an hour.

Speculation that Edmonds might have been on her phone prompted MBTA officials to issue a new warning to T operators to put down their cell phones. The use of cell phones is considered a safety violation, and can lead to suspension and firing.

Leone said there was also no evidence that Edmonds was in the process of using the Internet on her cell phone before the crash.

“In short, we found no affirmative evidence that the driver was using her cell phone in the moments leading up to the collision nor that it was a factor in the crash,” Leone said.

Leone also said a preliminary examination by the medical examiner found there was no indication of alcohol or other drugs in the driver’s system at the time of the crash.

He said a full toxicology report will take weeks for the medical examiner to complete.

A final report from the NTSB could take 12-18 months.

Leone said investigators from his office recovered Edmonds’ cell phone at the scene and reviewed records of her phone calls and text messages as well as her Internet usage on the phone.

He said investigators also interviewed witnesses at the scene, and studied forensic examination of evidence and analysis of the accident reconstruction performed by the MBTA.

“It is our determination that there is no evidence of criminal conduct by any of the survivors of the crash,” he said. “Further, there is insufficient evidence of criminal conduct by the operator of the striking trolley car.”

Leone said his investigation is now closed.

NTSB spokesman Peter Knudson said the agency will review the information provided by Leone’s office and by any other state, federal or local agencies studying the crash.

“We will continue to look at all the facts to ensure that we have a comprehensive understanding of all the elements that could be factors in this accident,” Knudson said.

Knudson said the agency wouldn’t speculate about a possible cause, but said the focus on their investigation has largely narrowed to include the MBTA’s overall operations and human performance, which includes everything that the operator was doing.

MBTA General Manager Daniel Grabauskas said his agency will continue to work with the NTSB to try to determine the cause of the accident.