DENVER – Investigators believe at least one of the suspects in the STEM School Highlands Ranch shooting Tuesday stole the guns from the parents of the 18-year-old suspect, two sources with knowledge of the investigation told Contact7 Investigates Wednesday.

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 news conference that investigators were working with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) to determine how the suspects, an 18-year-old male and a juvenile female, obtained the weapons. He said at the time it was “too early to tell” if the suspects had assistance in obtaining the weapons.

The Federal Bureau of Investigation has also been brought in to assist local authorities in the shooting investigation.

The sources said Wednesday that they believe the parents of Devon Erickson, the 18-year-old suspect, bought the weapons legally. Denver7 cannot say whether the parents had the guns secured inside the home.

People under age 21 are not allowed to buy handguns in Colorado.

Kendrick Castillo, 18, was killed in the shooting and eight other students were injured. As of early Wednesday, three students were still hospitalized, authorities said.

Sources told Denver7 Tuesday that the motive of the alleged shooters went beyond bullying and involved revenge and anger towards others at the school and that at least one of the suspects was involved in legal and illegal drug use and had been in therapy. But Spurlock said Wednesday the incident was “too new” to establish a motive.

He also said authorities were “deep” in social media searches and analysis of the suspects’ phones and computers. Tuesday's shooting is the first since Columbine in which two shooters were involved.

Erickson was booked on 30 counts after his first court appearance, according to Colorado court records. Those include one count of first-degree murder after deliberation and 29 counts of attempted first-degree murder. He will be held without bond pending his next court appearance.

The judge in the case set the date of the return of his formal charges hearing for Friday at 1:30 p.m.

Authorities have not identified the juvenile suspect, saying only she was female. Sources told Denver7 late Tuesday that the juvenile suspect is in the process of transitioning from female to male. She also appeared in court Wednesday.

STEM School Highlands Ranch will be closed for at least the rest of the week, the district said Tuesday night.