A former student at Radford University in Virginia pleaded guilty Monday to fatally stabbing her roommate.

Luisa Cutting, 21, pleaded guilty to second-degree murder in the Jan. 24 death of Alexa Cannon, a 20-year-old psychology major from Roanoke.

Cutting was sentenced to 40 years in prison, half of which is to be suspended after she serves 20 years, according to a Radford Circuit Court clerk. The judge also ordered that Cutting have no contact with Cannon’s family and that she undergo any mental health treatment recommended by authorities.

Cutting said in a brief statement Monday that she takes full responsibility for Cannon's death, according to NBC affiliate WSLS-TV in Roanoke.

Luisa Cutting. Radford City Police Department

"There are no words for this tragedy and my heart is filled with sorrow and grief," Cutting said. "My heart goes out to the Cannon family. I am so, so sorry."

Radford City Commonwealth's Attorney Chris Rehak said Cutting offered no motive for the crime.

When officers arrived at the off-campus apartment the two women shared, Cutting was covered in blood, turned around, put her hands behind her head and said, "Arrest me," Rehak said.

During interviews with police after her arrest, Cutting was incoherent at times and mentioned the apocalypse and said she did "cocaine with the devil," WSLS reported.

The commonwealth's attorney said Cutting admitted to taking a combination of alcohol, tobacco, marijuana, Adderall, Xanax, mushrooms and cocaine the night before the murder.

All of this, combined with a lack of sleep perhaps over a span of days, triggered a psychotic episode that the prosecution and the defense blamed for Cannon's death, according to WSLS.

"Now that she's stabilized, she hasn't had drugs in the many months that she's been incarcerated, the unfortunate thing is now what can she do?" defense attorney Blair Howard told reporters Monday. "And there's nothing she can do, except express her sincere sorrow to her family. That's all she can do."

The plea agreement spared Cutting's family and friends the anguish and the anxiety of a trial, Rehak said in a statement Monday.