A quiet university town is struggling to comprehend the violent murder of a 20-year-old woman at the hands of her best friend and roommate.

Luisa Ines Tudela Harris Cutting, 21, has been charged with second-degree murder after she called police to the apartment she shared with best friend Alexa Cannon, 20, in Radford, a small town in the US state of Virginia.

When police arrived at 7.45am on Thursday, they found Cutting covered in blood beside Cannon’s body, who had been stabbed 30 to 40 times.

According to a police warrant obtained by local media, Cutting instructed officers “arrest me”. When they asked why, she responded “I killed her.”

Items seized from the scene included a butcher’s knife, a serrated knife, pills, smoking devices and a “brown chalk-like substance”.

Social media posts by both women, who attended Radford University, paint the picture of a close friendship.

In an Instagram post from March 2018, Cannon shared a selfie of the pair together and described Cutting as like a mother to her.

“I met this girl two years ago online and somehow we ended up living across from each other for a year, this summer she was equivalent to my mom in Cancun,” she wrote.

“And unimaginably she still puts up with me and now we’re living together next year.”

In an eerie foreshadowing, she signed off “Love you more Lu and everyone pray that we don’t kill each other this year.”

Some posts by Cutting took a dark tone in recent weeks.

“I know death is coming but I still can’t wrap my head around it,” she tweeted on January 10.

On the 12th of January, she expressed frustration that Cannon had apparently not paid the apartment’s gas bill.

“My roommate forgot to pay the gas bill and they won’t come turn it on until Monday and now there’s a snowstorm on the way we’ll thank god I’ll be drunk all day.”

Friends of the students are stumped by the tragic turn their friendship took.

“I really wanna know what was the motive behind it because they were best friends since Freshmen year, and that was in 2016. Now it’s 2019 and this has happened,” Shelton Lewis, a Radford University junior, told local WDBJ7.

In a statement, Radford University president Brian Hemphill said “this is a difficult day for all involved,” the Roanoke Times reports.

“Alexa … was very involved on campus and was a proud member of several organisations … Alexa had a full life ahead of her, a life poised to make a great impact on those she would have encountered, the career she was pursuing and the communities in which she would have lived.”

If you are experiencing mental health issues or suicidal feelings contact Lifeline on 13 11 14 or BeyondBlue 1300 224 636. If it is an emergency please call 000.