A jury found Steven Briel guilty Wednesday of first-degree murder, strangulation and abduction in the death of a University of Mary Washington student last year.
Grace Mann, 20, was killed April 17, 2015, at the Fredericksburg, Virginia, home she shared with Briel and two other roommates.
The jury recommended Briel be sentenced to life in prison with an additional 11 years.
Much of the courtroom was in tears during the verdict, and jurors passed tissues to each another.
"All I ever wanted to do was be Grace's dad," Mann's father, Thomas Mann, said in a statement. "I want my daughter back."
"How do I explain to you what we've lost? How do I explan the hole in my arms and the hole in my heart," Melissa Mann, the victim's mother said.
The defense spent the first three days of his murder trial trying to show Briel was insane at the time.
"It's clear something is deeply and disturbingly wrong," defense attorney Mark Gardner said in his closing argument. "How could he be afraid of these young women? It's what most of us would say sounds insane. He's lost his damn mind."
In her closing argument, prosecutor La Bravia Jenkins urged jurors to reject the insanity defense, saying, "To make an excuse is inexcusable ... For a jury to accept that excuse would be dangerous for all of us."
Deliberations began shortly after 5 p.m. and lasted about three hours.
Dueling Diagnoses From Forensic Scientists
Forensic psychiatrist, Dr. Eileen Ryan, testified Wednesday that Briel did not understand the nature, character and consequent of his actions - the definition of insanity.
Ryan said Briel believed Mann had been tasked with killing him and was pumping poisonous gas into his bedroom.
When Mann returned home the day of her death and walked closely by Briel, he believed she was moving in to kill him, so he pushed her away, she fought back, he put his hand over her mouth, she bit him and he strangled her.
"He believed he was incapacitating Grace in self-defense," Ryan said. "He believed in his delusional mind he was about to be killed."
The prosecution called its own forensic psychiatrist, Dr. Avram Mack, who testified he believes Briel was sane at the time of the attack and does not exhibit signs of schizophrenia.
The most powerful prosecution evidence came at the very end: A jailhouse phone call from Briel to his parents, recorded two weeks after Mann's death. Jurors heard a completely normal-sounding young man chatting and joking with his parents about books and jail food.
Briel's Mother Takes the Stand
Briel's mother, Mary Briel, took the stand for the defense Tuesday to explain her text messages with her son the day Mann was killed.
Mary Briel testified she began to worry about her son in the weeks before Mann’s death. When he sent his parents a rambling, troubling email, Mary Briel testified she thought he might kill himself. He also expressed concerns about his roommates.
His mother recalled a visit home five days before Mann’s death.
"He did mention he felt the girls were going to kill him and make it look like a suicide," she testified.
Steven Briel’s parents urged him to give his roommates notice and move out. The morning of Mann’s death, he confirmed plans with his mother to take the train home, she testified.
That afternoon, he sent a text message saying he was cleaning the house. During the following 30 minutes, Mann was strangled.
Steven Briel then sent another message to his mother, writing, “Hey, made a mess. Someone's at the door knocking. What should I do? Run?"
She wrote back, "Are you serious? Don't answer.”
A few minutes later she wrote, “What the hell are you on? This is not funny.”
“I know. I'm scared,” he replied.
“Pack your clothes and get to a coffee place until the next train comes. Stat!!!!” Mary Briel texted back.
She testified Tuesday she did not know what he was scared about at that moment.
He would send her another text, writing, “Hey, I'm in the woods. What should I do?”
“Get to the bus. You still have time,” she wrote back.
When she got home a short time later, she got a message from Fredericksburg police and learned her son was accused of murder.
Grace Mann’s Best Friend Testifies About Confronting Accused Killer
Before the defense began its case Tuesday, Mann’s roommate Kathryn Erwin testified for the prosecution about confronting Steven Briel, introducing herself as Mann’s best friend.
She testified she received puzzling text messages from Briel as she and another roommate walked home that afternoon.
"I made a mess in Holly's room," texted Briel, referring to roommate Holly Aleksonis. Once the roommates were in the house, Briel emerged from a room.
"He'd sweated through his shirt. He seemed confused,” Erwin testified.
Briel then asked what she would you do if Mann wasn't there anymore.
Erwin testified she demanded to know what was going on, and Briel answered, “Grace came home and was a b---- to me. I slapped her. She bit me. So I strangled her.”
Erwin said she ordered Briel to go upstairs to his room, then she spotted Mann, whose skin was blue.
Mann’s parents broke into tears as prosecutors played Erwin’s 911 call. She can be heard counting out her CPR compressions -- the number rising higher and higher -- with no response from Mann.
Grace Mann's Roommate Testifies on First Day of Murder Trial
Aleksonis testified Monday about returning to the home and finding Briel drenched with sweat and speaking very quickly. She testified he stood before a closed bedroom door and said, "Grace and I got in an altercation. She hit me so I had to defend myself ... She bit me. What would you do if she weren't here anymore?'"
Aleksonis opened the door and saw her purple comforter on the floor.
"I pulled the comforter off," Aleksonis testified, "and Grace was there with a plastic bag over her head. I pulled it off and screamed and ran from the room."
As many in the courtroom sobbed, prosecutors played the 911 call from Aleksonis that day. She was so distraught, the dispatcher had trouble getting information until Aleksonis finally shouted, "My roommate strangled her!"