When the preliminary report into the crash of Air India Flight 171 - which killed 260 people in June - was released, many hoped it would bring some measure of closure.

Instead, the 15-page report further stoked speculation. For, despite the measured tone of the report, one detail continues to haunt investigators, aviation analysts and the public alike.

Seconds after take-off, both fuel-control switches on the 12-year-old Boeing 787 abruptly moved to "cut-off", cutting fuel to the engines and causing total power loss - a step normally done only after landing.

The cockpit voice recording captures one pilot asking the other why "did he cut-off", to which the person replies that he didn't. The recording doesn't clarify who said what. At the time of take-off, the co-pilot was flying the aircraft while the captain was monitoring.

The switches were returned to their normal inflight position, triggering automatic engine relight. At the time of the crash, one engine was regaining thrust while the other had relit but had not yet recovered power. The plane was airborne for less than a minute before crashing into a neighbourhood in the western Indian city of Ahmedabad.

Several speculative theories have emerged since the preliminary report - a full report is expected in a year or so.

The Wall Street Journal and Reuters news agency have reported that "new details in the probe of last month's Air India crash are shifting the focus to the senior pilot in the cockpit".

Italian newspaper Corriere della Sera claimed that its sources had told them the first officer repeatedly asked the captain why he "shut off the........

© BBC