Man is Accused of Suffocating Woman Before Texting Their Roommate: 'I Made a Mess'

(INSIDE EDITION)- A Virginia man accused of murdering a 20-year-old woman and then texting one of their roommates that he "made a mess" in her room, will use an insanity defense in his trial, according to reports.

Steven Vander Briel, 30, was charged with first-degree murder, strangulation and abduction in the April 17 killing of his roommate Grace Rebecca Mann, a University of Mary Washington student majoring in history and American history. He has pleaded not guilty.

Vander Briel's attorney filed a notice of insanity defense on Tuesday, NBC Washington reported.

The prosecution is expected to seek its own court-ordered mental evaluation of Vander Briel.

One of the other women Vander Briel and Mann lived with testified that he texted her that day asking when she and their fourth roommate would be home.

He allegedly wrote, "I was in [victim roommate]'s room and I made a mess," NBC wrote.

The roommates, Holly Aleksonis and Katheryn Erwin, reportedly said they went home, knocked on the bedroom door and a very sweaty Vander Briel slipped out of the room.

Erwin testified he was acting "neurotic, manic" and was making confusing statements, the Washington Post reported.

"What would you do if Grace wasn't here anymore?" he allegedly asked the pair before leaving the home. The roommates then found Mann's lifeless body.

Mann was lying near a bed under a purple comforter, her hands bound with a sweater and belt and her head covered by a plastic shopping bag, according to reports.

More bags were found shoved in her mouth, the Post wrote.

The women testified that Vander Briel said he and Mann had an altercation.

He said he had slapped Mann, that she bit him and then he strangled her, one of the women reportedly testified.

Vander Briel's alleged motive is still unclear.

Mann was an openly gay, popular student who served as an executive board member of Feminist United. Dubbed a "remarkable leader" of the organization, she had also recently been appointed to the President's Task Force of Sexual Assault.

"She was an amazing, genuine person who believed in equality and fought for it!" wrote the Rappahannock Council Against Sexual Assault, an organization that Mann's parents asked donations be made to in their daughter's name.

"I've known Grace for a long time and still cannot fathom why anyone would do such a thing to anyone, let alone the woman who inspired me every day for the past six years," one person wrote on a page created for donations.

Another person added: "Thank you for your strength, compassion and efforts to make this place a better world for women. I truly hope you are in a better place and at peace."

For more from INSIDE EDITION check them out online, or on FOX 29 weeknights at 6:30 p.m.