Former Metro general manager Richard Sarles (James A. Parcell for The Washington Post)

Witness interviews are a key part of the National Transportation Safety Board’s probe into a fatal smoke incident on D.C.’s Metro system. Each interview helps investigators put together a picture of what happened.

As part of their examination of January’s deadly smoke incident, which killed one rider and injured scores more, officials with the NTSB interviewed more than a dozen Metro officials, but former general manager Richard Sarles wasn’t among them, and some Metro watchers wondered why.

The 6,000 pages of documents made public by NTSB last week include interviews with senior Metro executives whose responsibilities include systemwide safety, power systems,  emergency ventilation, maintenance and control of rail operations — all areas that have emerged as likely factors in  the disaster.

[In first day of hearings, NTSB grills Metro officials over fatal smoke incident]

The NTSB did not interview Sarles, however, who had announced in September that he would retire from Metro. His final day at the transit agency was Jan. 16 — four days after the fatal Jan. 12 smoke incident that killed one person and sickened scores of others.

Sarles, who first served as Metro’s interim general manager following the fatal Red Line crash at Fort Totten that killed eight passengers and a train operator, was later made the transit agency’s permanent general manager.

NTSB spokesman Peter Knudson said that “initial interviews following an accident are usually focused around those who had some sort of operational role in the accident or the circumstance related to it.  In hearings, we tend to focus on key players in the organization, often in managerial/decision-making positions.”

Interviews with Metro personnel, including the operator of the stranded train and controllers who work in the transit agency’s central train control center, known as the ROCC, revealed a chaotic and fragmented response to reports of smoke in a tunnel just outside the L’Enfant station. Officials with the Washington Metropolitan Area Transit Authority have since made a series of changes designed to improve the agency’s response to future incidents and to improve the overall safety of the Metro system. Most recently, Metro announced that it would host a fire official at the ROCC  on most days, not only during emergencies. Currently, the District or Prince George’s County sends fire officials to the ROCC when there is an incident.

[Train operator said he heard yelling, screaming as smoke poured into stalled train]

Fire departments have lobbied for a broader presence for years and hope to eventually be in the ROCC 24/7. For now, however, a fire official will be in the ROCC  40 hours a week, with Metro covering the cost. Beyond immediate crises, the on-duty fire official will also use the time to help improve training for controllers on emergency command and control issues.