KUALA LUMPUR, Malaysia -- "All right, good night" were the final words heard by air traffic controllers from the missing Malaysia Airlines flight before it vanished over the South China Sea five days ago, relatives of the passengers were told Wednesday.
News of the last communication came as Malaysia defended its handling of the hunt for the missing Boeing 777 but acknowledged it is still unsure which direction the plane was headed when it disappeared, highlighting the massive task facing the international search.
Government officials said they asked India to join in the search near the Andaman Sea, suggesting they think the jetliner and the 239 people on board might have reached those waters after crossing into the Strait of Malacca, some 250 miles from the flight's last known coordinates.
The mystery over the plane's whereabouts has been confounded by confusing and occasionally conflicting statements by Malaysian officials, which have led to allegations of incompetence or even cover-up, adding to the anguish of relatives of those on board the flight, two thirds of them Chinese.
"There's too much information and confusion right now. It is very hard for us to decide whether a given piece of information is accurate," Chinese Foreign Ministry spokesman Qin Gang told reporters in Beijing. "We will not give it up as long as there's still a shred of hope."
CBS News correspondent Bob Orr says the U.S. government has offered wide-ranging assistance, including investigators from the FBI, FAA and National Transportation Safety Board.
On Wednesday, the NTSB said in a statement that its investigators with expertise in air traffic control and radar were providing technical assistance to Malaysian authorities. The investigators traveled to Kuala Lumpur during the weekend.
Malaysian Defense Minister Hishammuddin Hussein described the multinational search as unprecedented. Some 43 ships and 39 aircraft from at least eight nations were scouring an area of 35,800 square miles to the east and west of Peninsular Malaysia.
"It's not something that is easy. We are looking at so many vessels and aircraft, so many countries to coordinate, and a vast area for us to search," he told a news conference. "But we will never give up. This we owe to the families of those on board."
Malaysian officials met in Beijing on Wednesday with several hundred Chinese relatives of passengers to explain the search and investigation. They said the last words from the cockpit to Malaysian air traffic controllers before the plane entered Vietnamese airspace were, "All right, good night," according to a participant in the meeting. Vietnamese officials said they never heard from the plane.
Malaysia Airlines flight MH370 took off from Kuala Lumpur for Beijing early Saturday and fell off civilian radar screens at 1:30 a.m. about 35,000 feet above the Gulf of Thailand between Malaysia and southern Vietnam. It sent no distress signals or any indication it was experiencing any problems.
Malaysian authorities said Wednesday that a review of military radar records showed plots of what might have been the plane turning back, crossing over the country and flying to the Strait of Malacca, a busy shipping lane west of the narrow nation.
Air force chief Gen. Rodzali Daud said the radar showed an unidentified object at 2:15 a.m. about 200 miles northwest of Penang.
"I am not saying it's flight MH370. We are still corroborating this. It was an unidentifiable plot," he said.
Military and government officials said American experts and the manufacturer of the radar systems were examining that data to confirm whether it showed the Boeing 777. Until then, they said the search would continue on both sides of the country.
It's unlikely the plane would have flown across Malaysia without being detected by civilian radar unless its electrical systems, including transponders allowing it to be identified by radar, were either knocked out or turned off.
Orr says veteran crash investigators have been confounded by the Malaysian military reports on the radar sighting.
If it did in fact change direction so dramatically to the southwest, the jet might have flown hundreds of miles off course without maintaining radio or data contact with controllers.
For that to be possible, experts say the plane must have either suffered an electrical failure that disabled the transponder which reports location, altitude, and speed, or somebody in the cockpit deliberately turned it off. Orr says that's why investigators cannot rule out hijacking or a criminal act by the flight crew at this stage.
Authorities in fact haven't ruled out any possible cause, including mechanical failure, pilot error, sabotage or terrorism. Both the Boeing 777 and Malaysia Airlines have excellent safety records. Until wreckage or debris is found and examined, it will be very hard to say what happened.
Malaysia said India was joining the search in waters near the Andaman Sea. "As of today, we have not found anything, but we are extending (the search) further," Hishammuddin said.
Confusion over whether the plane had been spotted flying west prompted speculation that different arms of the government might have different opinions about its location, or even that authorities were holding back information.
Earlier in the week, Malaysia's head of civil aviation, Azharuddin Abdul Rahman, was asked why the Strait of Malacca was being searched and replied, "There are things I can tell you, and things I can't," suggesting that the government wasn't being completely transparent with its information.
On Wednesday, Gen. Rodzali released a statement denying remarks attributed to him in a local media report that military radar had confirmed the aircraft had made it to the Strait of Malacca. The Associated Press contacted a high-level military official who confirmed the remarks.
Asked about this, Hishammuddin said his government had been transparent from the start.
"There is only confusion if you want to see confusion," he said. "Basically we have been very consistent on what we've been saying the last few days."
If all those on board are confirmed dead, it would be the deadliest commercial air accident in 10 years.
Choi Tat Sang, a 74-year-old Malaysian man, said his family is still holding out hope that the plane and all on board are safe. His daughter-in-law, Goh Sock Lay, 45, was the chief stewardess on the flight. Her 14-year-old daughter, an only child, has been crying every day since the plane's disappearance.
"We are heartbroken. We are continuing to pray for her safety and for everyone on the flight," he said.