Details are still unclear about the course of the shooting at a school in Madison, Wisconsin, in which three people – including the 15-year-old shooter – died and several others were injured on Monday.

Police said Natalie Rupnow, who called herself Samantha, killed a teacher and a fellow student with a pistol in the shooting.

Rupnow died of a self-inflicted gunshot wound before officers arrived at the school, police said. The officers did not fire their weapons.

Two students suffered life-threatening injuries and are in critical condition, while a teacher and two other students were treated for non-life-threatening injuries.

In a news conference Monday, police said the shooting was confined to “one classroom in a study hall full of students of various grade levels.”

Police have not yet given a motive for the attack or said whether they believe the victims were targeted.

Madison Police Chief Shon Barnes said Monday, “I don’t know if (the shooter) was transgender or not,” adding that speculation about Rupnow’s background had no significance to authorities at the time.

“I don’t think what happened today had anything to do with how she or he or they wanted to identify,” Barnes added.

The suspect’s father reportedly spoke to police at one of their facilities shortly after the incident. Police are “trying to figure out what he knew or didn’t know about what happened today, but again, he lost someone,” Barnes said.

“The parents are cooperating fully. We have no reason to believe at this point that they committed a crime,” Barnes said.

A second-grader made the 911 call, Barnes said. “Let that sink in for a minute,” Barnes added. “A second grader called 911 at 10:57 a.m. to report a school shooting.”

President Joe Biden called the incident “shocking and incomprehensible” in a statement Monday evening, calling on Congress to act “now.”

He insisted they pass “common sense” gun safety laws, including universal background checks, a national red flag law and a ban on both assault weapons and high-capacity magazines.

“It is unacceptable that we cannot protect our children from this scourge of gun violence,” the statement said, adding: “We cannot continue to accept it as normal.”

Biden also noted his administration’s efforts to combat the gun violence epidemic in the United States, including the creation of the White House Office to Prevent Gun Violence, said more needs to be done and offered his prayers to those affected in Madison.

Wisconsin Gov. Tony Evers said in a statement, “There are no words to describe the devastation and heartache we feel,” calling the shooting a “harrowing tragedy.”

Evers said he and his wife are praying “for the families and loved ones of those whose lives were so senselessly taken, as well as for the educators, staff and the entire Abundant Life school community.”

“It is unthinkable that a child or a teacher would wake up one morning, go to school and never come home again,” he said. “This should never happen, and I will never accept this as a foregone conclusion or stop working to change it.”