“Maybe it’s the time to murder her.”

That’s the thought that, according to police, popped into Eduardo Arevalo’s head on Dec. 16 after an argument with his pregnant sister, Viridiana.

An affidavit made public on Monday alleges that Eduardo approached his older sister as she sat on the couch in their home in a Dallas suburb called The Colony, crooked his right arm around her neck, and squeezed the life out of her.

Then the 19-year-old tossed her in his car trunk, drove to a field, and dumped her body, police said. He allegedly returned a few days later to move the corpse to an alley—then capped off the grisly task with a stop at Whataburger.

Police say the motive for the murder was embarrassment: Eduardo felt the 23-year-old had shamed the family with her pregnancy. “It would be better off that she wasn’t here,” he allegedly later told police.

But at the time of Viridiana’s disappearance, Eduardo hoped to make it look like a suicide, police said. The victim reportedly suffered from depression, and her brother allegedly manufactured a note in which she appeared to write about wanting to take her own life.

That didn’t add up for police, though, and they began to suspect Eduardo had a hand in Viridiana’s death. Surveillance video near the alley where her body was found helped them crack the case. Then Eduardo confessed, they said.

“I murdered her, I murdered her,” he allegedly told detectives.

Despite the confession, Eduardo’s brother, Diego Arevalo, told KXAS he believes he’s innocent.

“It doesn’t make sense that my brother would do something like this. He was either set up or something happened,” Diego said.

“I know my brother, he wouldn’t do something like this. He’s very kind, very positive kind of guy, very motivated. He helped my family out, he helped my brothers, he even helped my sister out,” he told KTXA.

Eduardo Arevalo was charged with capital murder because his sister was eight months pregnant, and he was held on $1 million bail.

Sgt. Aaron Woodard of The Colony police department told the Dallas Morning News that the case was a a difficult one for investigators.

“It’s not what our officers and detectives wanted to be dealing with two days before Christmas,” he said.