TELLURIDE, Colo. (AP) — One student was responsible for threatening a "Columbine-style" attack at a high school in the Rocky Mountain resort town of Telluride, authorities said as classes resumed Tuesday.

Police haven't made any arrests in connection with the threats that shut down the school on Monday and haven't yet requested any charges.

The male student was released to his parents Monday night and has been suspended from school, according to a statement released by the San Miguel County Sheriff's Office on Tuesday. His name and age have been withheld.

Police believed there may have been more than one person writing the threats based on students' initial reports of the messages. But after interviewing several students who saw the messages, police now believe the lone male student sent a message about explosives at the school using Snapchat and then referenced the Columbine shooting in a conversation within the app.

"We are confident we have interviewed the individuals who were involved in the conversations and the single author of the threats," Telluride Chief Marshal James Kolar said. "This is an ongoing investigation, but we are satisfied that there is no imminent threat to the school, students or community."

Police were able to capture a copy of the explosives threat and plan to get a warrant for the later reference to a shooting, the statement said.

Classes resumed Tuesday at Telluride High School under heightened security and police likely will remain at the school all week.

Multiple agencies, including the FBI, searched the school for hours on Monday but found no weapons or explosives.

A rifle and a handgun that was locked up were seized at the student's home. The sheriff's office said "no further evidence was found to indicate a plan, materials or ability" to carry out the threats.