On Tuesday, Alan Hruby, 19, confessed to killing his parents, John, 50, and Joy, 48, as well as his sister, Katherine, 17, at their home, according to police.
Their bodies were discovered in the kitchen just a day before Hruby's shocking admission, when the family's housekeeper walked in on the violent scene.
Hruby, a student at the University of Oklahoma, told investigators he shot his mother first, according to court documents obtained by PEOPLE.
When she did not die of the first shot, he fired a second time "while she was lying on the floor," the papers state.
Hruby, who used a 9mm pistol taken from his father's truck, shot his sister next when she "came into the house from washing her vehicle," the documents read. Hruby "believed death to be immediate."
His father John showed up an hour after the first two murders. Hruby fired twice on his father, noting that his father "stated, 'Ouch,' and fell to the ground" after the first shot, according to court documents.
Hruby then fired a second round into his father to kill him.
When asked by authorities why he killed his family, Hruby said he "had been cut off financially … due to an abundance of spending in recent times," the papers state.
"He explained that there was a loan shark company in Norman, Oklahoma, that he owed approximately three thousand dollars to," Stephens County District Attorney Jason Hicks told Oklahoma News Channel KFOR.
Added Hicks: "He felt like if he murdered his mother, his father and his sister, he would be the only one, the only heir, to their estate."
While the teen initially seemed "distressed" by his family's murder when he arrived at the police station on Oct. 13, Police Chief Danny Ford told PEOPLE, "Some of the timelines and things that he was giving us were not matching up with information that we had."
They held him for further questioning and he eventually confessed to the killings.
According to police, the murders took place Oct. 9. After the shootings, Hruby spent the weekend in Dallas, where he attended the Oklahoma University-Texas football game, even posting a picture to Instagram captioned: "College wouldn't be half as great with out these two peaches."
College wouldn't be half as great with out these two peaches. #bestfriends #roomies #college #outx #ou #universityofoklahoma
Apart from a stolen check complaint, there was nothing to indicate that Hruby was capable of such violence, Ford said.
"We've had people out in the community that have given us information that he was giving Mom and Dad some trouble, but we've not had much contact with him that I'm aware of," he said. "The credit card and the checks were the first I've heard of it."
"There's people that are shocked. They're having a hard time grasping that this would happen – in the community, first, and second, to this family."
But Hicks said Hruby has shown no real grief over his family's deaths, adding, "The only remorse we’ve seen is because he got caught," he told KFOR.
"Any tears that he shed, they were crocodile tears," he said. "It wasn't remorse because 'I've lost my mom, my dad and my sister,' it's remorse because he knows that his life is basically over."
Hruby's attorney did not immediately return calls for comment.
Stephens County Jail