The father of the alleged teenage gunman who killed four people in a Georgia school shooting on Wednesday told police this week that he gave the boy the AR-15-style rifle used in the massacre as a Christmas present last year, law enforcement sources told The Post.

Suspected gunman Colt Gray, 14, fired a hail of bullets into Apalachee High School in Winder on Wednesday morning, killing two students and two teachers before he was arrested, authorities said.

The AR-15-style rifle reportedly used in the horrific shooting was given as a gift just seven months after the FBI visited Gray and his father Colin in May after receiving tips about online threats of school shootings, the agency said.

According to a statement from the Atlanta office, online posts sent to the agency last year included images of weapons.

Jackson County sheriff’s detectives identified Gray, then 13, as a possible suspect, but after questioning him and his father, law enforcement officials saw no reason to take further action, the FBI said.

Colin Gray told police at the time that he had shotguns in his home, but Colt did not have unescorted access to them, authorities said. The teen also denied making the threats.

But more than a year later, Gray allegedly opened fire at his high school, killing 14-year-old students Mason Schermerhorn and Christian Angulo and math teachers Richard Aspinwall, 39, and Christina Irimie, 53, authorities said.

Another eight students and a teacher were injured in the mass shooting.

Gray is charged with four counts of murder in connection with the shooting, according to police.

The Post reached out to Colin Gray for comment on Thursday, but to no avail.