MIDLAND, Texas — A soldier accused of bringing explosives into an airport in his carry-on bag may have flown halfway across the country with them the week before, according to what he told investigators in court documents.

Trey Scott Atwater of Hope Mills, N.C., was to make his initial federal court appearance today. Authorities say the 30-year-old went through a security checkpoint Saturday at Midland International Airport with C-4, a powerful explosive.

He has been charged with trying to bring explosives onto an airplane, which carries a maximum 10-year federal prison sentence.

Atwater, based at Fort Bragg, N.C., told the FBI he is a demolitions expert who returned from his third deployment to Afghanistan in April, according to court documents. He said his Army special forces team always carried at least two blocks of C-4, but he didn’t know any explosives were in his bag when he returned to the U.S.

He said any explosives in the main compartment of the bag when he packed for his trip to Texas. The bag had been in his garage and hadn’t been used since he returned from overseas, according to court documents.

Atwater was detained at the Fayetteville, N.C., airport on Dec. 24 when security agents found a military smoke grenade in his carry-on bag, according to court documents. The documents don’t say whether officials now suspect C-4 may have been in his bag then but was missed during additional screening or whether the grenade and C-4 were found in the same bag, although at different times.

After the grenade was confiscated, Atwater was “admonished” and allowed to continue on to Texas, the documents said. He was stopped at the Midland airport Saturday, when he and his family were heading home. A TSA agent spotted a suspicious item in Atwater’s carry-on bag during screening, and a police bomb squad identified that as C-4.

The FBI didn’t find out about the grenade incident until being informed by the Transportation Security Administration after Atwater’s arrest in Midland.

“When I asked him about the December 24 Fayetteville incident after TSA informed me of it, Atwater acknowledged that it had occurred, but said he had forgotten to mention it to us during our initial interview,” the FBI agent wrote in the affidavit filed in the case.

No one answered the door today at the home of Atwater’s parents in a quiet middle-class neighborhood in Midland, about 320 miles west of Dallas. An American flag between the two garage doors fluttered in the breeze.

A neighbor who lives two doors down, Pam Moore, 55, said she watched Atwater grow up. She said he was a “wonderful kid” who played high school football.

“We were real proud of him when he joined the military,” Moore said. “I feel sorry that he got caught up in this. … I just hope everything works out for him. I really do.”