A 20-year-old college student in Iowa who was charged with shooting and killing his parents and sister at their family home this week told police that a masked man committed the triple murder, according to a criminal complaint released Wednesday.

Alexander Jackson called police Tuesday morning to report that a male intruder had broken into his family’s Cedar Rapids home and shot him and his dad, the complaint said.

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Cedar Rapids police said responding officers found the bodies of 61-year-old Jan Jackson, 68-year-old Melissa Jackson and 19-year-old Sabrina Jackson in different rooms of the home. They had all suffered gunshot wounds.

Alexander Jackson suffered a gunshot wound to his foot and was treated at a hospital, police said.

Alexander Jackson, an Eagle Scout and a student at the University of Iowa, was charged with first-degree murder in the shooting deaths of his parents and younger sister at their home in  Cedar Rapids. (Linn County Correctional Center)

However, the complaint said police found no signs of forced entry or burglary at the home and recovered a .22 caliber semi-automatic rifle that is believed to have been the firearm used in the shootings.

After having his foot treated at the hospital, Alexander Jackson was taken into custody and charged with three counts of first-degree murder in the deaths of his family, police said.

Assistant Linn County Attorney Ryan Decker described the incident as "a horrendous murder" during the suspect’s first appearance in district court Wednesday morning, The Gazette newspaper in Cedar Rapids reported.

"This was more than just a murder – it was an execution of the defendant’s mother, father and sister," Decker said. "Furthermore, the defendant’s concocted story of a phantom burglar shows the defendant acted out of malice and calculated intent to get away with these murders."

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He denied shooting his family members, according to the complaint, but admitted that his father had recently told him he needed to find a job or move out of the home.

The complaint said Alexander Jackson told police that he woke up to the sound of gunfire and was shot during a struggle with a masked man over the rifle, which he claimed he and his father had left on the fireplace after cleaning it the previous night.

Jackson, an Eagle Scout and student at the University of Iowa, was being held on a $3 million bond.

If convicted of first-degree murder, he could face life in prison without a possibility of parole.

The Associated Press contributed to this report.