Midland County Sheriff's Office via The Odessa American, File, Associated Press
File - This undated file photo provided by the Midland County Sheriff's Office via The Odessa American shows U.S. Army Sgt. Trey Scott Atwater. Atwater 30, who was arrested after a powerful, military-grade explosive was found in his carry-on luggage at Midland (Texas) International Airport could learn Friday, Jan. 6, 2012 whether he'll be released from federal custody.

MIDLAND, Texas — A North Carolina soldier who allegedly told investigators he didn't realize he had military-grade explosives in his carry-on luggage after his detention at a Texas airport last weekend could learn Friday whether he'll be released from federal custody.

Sgt. 1st Class Trey Scott Atwater, 30, is charged with trying to bring explosives onto an airplane, which carries a maximum 10-year federal prison sentence. He was due to appear at a detention hearing in Midland later Friday, during which a federal magistrate could grant his release.

Atwater, a member of the Green Berets based at Fort Bragg, in North Carolina, was detained Saturday after Midland International Airport security officers found C4 explosives in his carry-on bag, authorities said. Atwater, who grew up in Midland and now lives in Hope Mills, N.C., was with his family and was trying to fly home after the holiday visit.

According to court documents, Atwater told FBI agents he's a demolitions expert and had returned from his third tour in Afghanistan in April. He said his Army special forces team always carried C4, which troops use to blow the hinges off doors or destroy unexploded ordnance, and that he didn't know it was in his bag when he returned from his most recent deployment.

Agents said he told them the bag had been in his garage since he returned from Afghanistan, and that he only checked the bag's main compartment when he packed Texas, so he wouldn't have seen them.

Rep. Mike Conaway, a Republican congressman from Midland, said Thursday that officials from the Transportation Security Administration and FBI told his office Atwater had two 2.5-pound blocks of C4 in his luggage. He said he believes Atwater's explanation.

"That's the most plausible explanation," Conaway said. "He just forgot about it."

Military officials are assisting in the investigation, but the Justice Department has jurisdiction, said Lt. Col. Tom Bryant, a spokesman for the U.S. Army Special Operations Command at Fort Bragg.

"It would be speculative for me to say whether it's going to be a federal prosecution or a military one," Bryant said.

Atwater also was detained at the airport in Fayetteville, N.C., the city adjacent to the sprawling Army post, on Dec. 24 when security agents found a military smoke grenade in his carry-on bag. After the smoke grenade was confiscated, Atwater was "admonished" and allowed to fly to Texas, according to court documents.

Typically, bags are thoroughly searched and placed on X-ray machines for a second time after a suspicious item is found, although court documents do not say whether that was done in Atwater's case.

Conaway said an investigation is being done at the Fayetteville airport to determine what TSA did after finding the smoke grenade.

"They will be reviewing surveillance tapes," he said.

C4 looks like a block of clay and requires a blasting cap or detonator to explode. Combat troops have ready access to the explosive, which can also be used as fuel for heating water or rations.

The U.S. military forbids troops from taking C4 out of combat zones, but the screening process for troops heading home is not as stringent as for people flying on commercial airlines.

C4 can be purchased legally by civilians who have, in the very least, explosives user permits, Tom Crowley with the Bureau of Alcohol, Tobacco and Firearms in Dallas said in an email. Most civilians who buy C4 are in law enforcement, are researchers or are people who use it for training, he said.

C4 used by the military is produced under a specific Department of Defense contract for military use only and is not for sale to the public, Crowley's email said.

AP Writer Martha Waggoner in Raleigh contributed to this report.

Associated Press writer Betsy Blaney can be reached at http://twitter.com/betsyblaney