SAN ANTONIO – A man arrested Sunday in connection with his wife's disappearance purchased cans of gasoline, heavy duty trash bags, work gloves, a portable burn barrel, a shovel and an ax -- all in an effort to get rid of his wife's body, authorities said.

Air Force Maj. Andre McDonald, 40, was charged Sunday with tampering with evidence after he tried to destroy a receipt for the aforementioned items, according to Bexar County Sheriff Javier Salazar.

Investigators said McDonald purchased the items Saturday morning after his wife, 29-year-old Andreen McDonald, was reported as missing by friends.

Asked whether he had anything to say about his arrest or to the couple's 6-year-old daughter, a handcuffed McDonald smirked and said, "I love my daughter. I love my family. That's it."

Salazar immediately described McDonald's disappearance as "very suspicious" after investigators recovered her purse, wallet, car keys and "anything that, typically, you would expect somebody to take with them if they were going to be leaving," Salazar said Saturday,

On Sunday, the case took a grim turn when the sheriff said investigators obtained evidence leading them to believe McDonald was killed. Additionally, Salazar said "it's pretty evident" that the couple's 6-year-old, who is on the autism spectrum and mostly nonverbal, witnessed her mother's presumed death.

Investigators with the Sheriff's Office spent Sunday combing through fields in the Wilderness Oak area off of U.S. Highway 281 with cadaver dogs, searching for McDonald's body. Salazar said deputies are focused on that area, which is close to the couple's home, because forensic evidence indicates the pair was there at some point.

According to authorities, Andre McDonald hasn't offered authorities much help in locating his wife.

"He asserted his right to counsel, which he absolutely has, but it made us a bit suspicious -- not the fact that he asserted his rights, the fact that he didn't seem to care very much at all that his wife was missing, and the fact that he just flat out refused to help us with finding her," Salazar said.

Deputies first detained McDonald Saturday afternoon, citing mental health concerns.

Authorities said they set up surveillance on the McDonalds' home and covertly followed him to a gun shop Saturday afternoon, where they said he hurriedly purchased a firearm and a significant amount of ammunition. According to Salazar, McDonald was in such a hurry, he left behind the firearm he had just purchased and his ID.

"At that point, we were not certain if there were some suicidal thoughts going through the subject's mind," Salazar said Saturday. "(Deputies) made contact with him outside the residence, took him into custody, detained him at that point due to a possible mental health issue."

On Sunday, however, Salazar said McDonald seemed of "pretty sound mind," adding that he felt McDonald was treating the investigation like a game.

"He's a highly intelligent person, and I think he knows exactly what he's doing," Salazar said. "I think that quite frankly, he probably thinks he's smarter than anybody in law enforcement, but he's behind bars right now."

Salazar said McDonald, a cyberwarfare specialist who has a background in engineering, was "kind of smirking, kind of laughing, like he got one over on everybody."

"I think it's pretty evident that we're not joking around with him because he's behind bars."

The sheriff said, should McDonald make bail, his conditions of release would include wearing a GPS monitor and staying under house arrest.