DENVER – Investigators believe the two suspects in the shooting at STEM School Highlands Ranch smashed into the locked gun cabinet at the home of the adult suspect’s parents Tuesday morning, stole the weapons and used them in the shooting later that day, a high-ranking source with knowledge of the investigation tells Denver7.

The source also told Denver7 that investigators believe the two suspects spray-painted “F--- society” and “666” on the vehicle of one of the parents and tried to set the vehicle on fire before they left to go to the school. Investigators are looking into whether the suspects were attempting to make the scene look like their actions at the school Tuesday came as the result of them being bullied, the source said.

High-ranking sources told Denver7 on Tuesday night that the motive of the alleged shooters went beyond bullying and involved revenge and anger towards others at the school.

Two sources with knowledge of the investigation told Denver7 on Wednesday that investigators believed the guns were stolen from the parents. But Denver7 could not report at the time the manner in which the weapons might have been secured.

The sources said Wednesday they believe the parents of the 18-year-old suspect bought the weapons legally and that the guns were stolen by the suspects. People under age 21 are not allowed to purchase handguns in Colorado.

Douglas County Sheriff Tony Spurlock confirmed at a news conference Wednesday morning that at least two handguns were used in the shooting. High-ranking sources told Denver7 Tuesday night that three handguns and a rifle were recovered but said the rifle was not used in the shooting.

Spurlock said at the same news conference that investigators were working with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to determine how the suspects obtained the weapons. The FBI is also helping investigate the shooting.

The car scrawled with graffiti was seen being taken from the home of the adult suspect’s parents the night of the shooting as investigators served a search warrant.

Both of the suspects made their first court appearances Wednesday. The adult suspect is being held without bond for investigation on one count of first-degree murder and 29 counts of attempted first-degree murder.

Kendrick Castillo, 18, was killed in the shooting and eight other students were injured. Castillo was one of several heroic students credited with charging one of the gunmen and perhaps mitigating the number of casualties.

Authorities are also investigating whether the armed guard at the school may have mistakenly fired at deputies who were responding to the shooting and whether one of the students was hit by a bullet from either the guard or a responding deputy. Spurlock has said the guard was instrumental in taking one of the alleged shooters to the ground, as well.

"I know that my client is a hero and I know that he did everything in his power to protect the kids, and the staff and the faculty that he knows and works with every day,” the guard’s attorney, Robert Burk, said in an interview Thursday.

A judge has sealed the underlying arrest affidavits or criminal complaints for the suspects while the early stages of the investigation continue.

Both suspects are due back in court Friday afternoon and are expected to be formally charged by prosecutors.