A 15-year-old girl was fatally stabbed by an intruder at a high school in Stockton, California, on Monday, according to officials.

The student was killed when a man in his 40s entered Stagg High School and stabbed her multiple times. Responders immediately began lifesaving measures, but she was pronounced dead at a local hospital, Stockton police said.

“A trespasser entered the front of our school today, stabbed one of our students multiple times,” Stockton Unified School District Superintendent John Ramirez Jr. said at a press conference. “Unfortunately, she did not make it. The assailant was taken, was detained, and taken into custody immediately.”

“The school was also put on lockdown to assure the safety of the rest of our students,” he added. “We began to work with local law enforcement immediately and they’ve taken over the investigation.”

Officials said they do not have a motive for the attack, but said the man was not a parent.

Ramirez praised the school’s resource officer for acting quickly to apprehend the suspect, saying it helped to prevent the stabbing from continuing.

“When the incident happened, there were staff immediately there,” he said. “It had been so quick that they weren’t able to stop it, but they were there immediately.”

Stockton Police Department Deputy Chief Eric Kane said they are still investigating the relationship between the girl and the unidentified attacker.

ABC News’ Matthew Fuhrman contributed to this report.