EVERETT — A Snohomish girl accused of stabbing two fellow students Monday was expelled from school last spring after other students complained that she had threatened violence.

The girl was allowed to come back to Snohomish High School only after school officials received a letter from mental health professionals concluding it was safe to allow the girl to return to classes.

Prosecutors on Wednesday charged the girl, 15, with attempted first-degree murder and second-degree assault in connection with the knife attack inside a bathroom at Snohomish High School.

A freshman girl, 14, was critically injured, suffering multiple knife wounds to her heart, lungs and throat. A second freshman, 15, was injured when she tried to stop the assault on her friend.

The suspect allegedly told investigators that she had planned to stab someone at school and had packed two knives in her backpack. Police believe she chose the victims at random.

Court documents released Wednesday said that the girl had been suspended from school in April. That unrelated incident involved two female students who reported that the suspect became obsessed with them and threatened to kill the boyfriend of one of the girls. The suspect was told she couldn’t come back to school until she received professional counseling. School officials received a letter from Fairfax Hospital in Kirkland, which specializes in behavioral health care, last April stating that the girl was safe to return to school, according to court papers.

She was allowed to return May 4.

A judge on Tuesday was told that the girl had been seeing a mental health professional and was taking medication before Monday’s incident. After her arrest, the girl told a detective she’d been contemplating suicide, according to court papers.

When investigators searched the suspect’s backpack, they found another knife and a notebook with the words “murder,” “tears” and “death” written in block letters.

The girl was being held Wednesday on $1 million bail at the Denney Juvenile Justice Center. Because of the serious nature of the charges, there will be a mandatory hearing to determine if the case belongs in adult court.

Doctors on Wednesday said the critically injured teen’s condition was improving. She was upgraded to satisfactory condition, said Cheri Russum, a spokeswoman from Providence Regional Medical Center Everett.

Police reported that when they found the stabbing victim Monday, she was on the bathroom floor under a sink, propped up against a wall. She had visible cuts to her neck and wrist. School staff applied pressure to the wounds. Paramedics quickly determined that the girl’s condition was grave and she couldn’t wait to be airlifted to Harborview Medical Center in Seattle. She was rushed by ambulance to Everett, where she underwent six hours of surgery to repair damage from up to 25 stab wounds.

Her 15-year-old friend had a severe gash to her forearm that required 20 stitches. She also had been stabbed in the back.

The friend told police that she and the 14-year-old were in the bathroom getting ready for school. She said she saw a stall door slowly open. She saw that the suspect had a knife in her hand and then heard her friend begin screaming, court papers said.

The girl ran out of the bathroom, yelling for help. She returned to the bathroom. She said she saw the suspect with a knife in her hand, standing over her friend.

Court documents released Wednesday also detail how other students came to the aid of the victims. One boy raced into the bathroom after hearing screams. He pressed a paper towel to the bleeding girl’s neck. Another boy also rushed into the bathroom. He told investigators that he saw the suspect looking at the victim, a bent and bloodied knife at her feet. He picked up the knife and tossed it away from the suspect. He then called 911.

A security officer escorted the suspect to the principal’s office.

The security officer told investigators that the suspect shrugged her shoulders when he asked why she had attacked the other girls, court papers said.

Diana Hefley: 425-339-3463; hefley@heraldnet.com.