CAPE CANAVERAL, Fla. - The spacewalking astronaut who came close to drowning in a flooded helmet searched for clues in his spacesuit Wednesday in hopes of understanding the unprecedented water leak.

Engineers in Houston, meanwhile, conducted their own investigation into what should have been a routine, yet still risky, maintenance job outside the International Space Station.

But a day after one of NASA's most harrowing spacewalks in decades, answers eluded the experts.

"There still is no smoking gun or definite cause of what happened or why that water ended up" inside Luca Parmitano's spacesuit, said NASA spokesman Kelly Humphries.

Parmitano, Italy's first and only spacewalker, could not hear or speak by the time he re-entered the space station on Tuesday, 1 1/2 hours after stepping out. He also had difficulty seeing because of the big globs of water in his helmet and elsewhere in his suit.

He'd worn the same suit on a spacewalk a week earlier, without mishap.

NASA aborted the second spacewalk because of the deluge and later acknowledged it was a serious situation in which Parmitano could have choked or even drowned. He looked all right, although wet, when his crewmates pulled off his helmet, and was reported to be in fine shape.

On Wednesday, Parmitano shined a flashlight through the ring collar of his suit. His colleague, American Christopher Cassidy, examined other equipment.

Nothing suspicious popped up, Humphries said.

There are only two sources of water in the suit: a 32-ounce drink bag and a 1-gallon cooling system embedded in long underwear.

NASA has pretty much ruled out the drink pouch. That leaves the cooling system. Specialists detected a higher than normal usage of water from the system's tanks, which could be consistent with Tuesday's leakage, Humphries said.

"No real theory yet on exactly where this water came from or why, but they are doing a very deliberate, step-by-step process of troubleshooting," he said.

Tuesday's close call points out the ever-present dangers of spacewalking, Mission Control managers acknowledged to reporters following the episode.

The next NASA astronaut set to fly to the space station, Michael Hopkins, said the important thing is that the spacewalkers got back in safe, thanks to everyone's quick, appropriate reactions. While "certainly concerned" by Tuesday's events, he said he's confident the mystery will be solved before NASA sends anyone else out the hatch.