Norman, Oklahoma - A man accused of beheading a co-worker was convicted of first-degree murder on Friday for the 2014 attack that one witness said was "something that people shouldn't have to see".Jurors deliberated for about two hours before finding 33-year-old Alton Nolen guilty in the death of 54-year-old Coleen Hufford. Jurors also convicted Nolen of assault and battery with a deadly weapon for attempting to behead a second co-worker at the Vaughan Foods plant in Moore, a suburb of Oklahoma City.Prosecutors have said they would seek the death penalty.Investigators said Nolen had just been suspended from his job when he walked inside the company's administrative office and attacked Hufford. Authorities said Nolen stabbed another co-worker, who survived. A company executive then shot Nolen.Hufford's daughter, Kelli Hufford, released a written statement on behalf of the family on Friday, saying the verdict helps them move toward closure."This has been a long road for my family and me," the statement read. "We are thankful the jury found Alton guilty of murder. All of us now hope for a swift sentencing process concluding with the death penalty for this killer."During the trial, prosecutors played recordings of Nolen confessing to the stabbings while he was hospitalised following the attack. In the recordings, Nolen says he doesn't "regret it at all" and that "oppressors don't need to be here".Mentally illNolen's attorneys say he's mentally ill and that he believed he was doing the right thing because of his delusional misinterpretations of the Quran. But prosecutors said Nolen knew right from wrong before he attacked Hufford, and Oklahoma City television station KFOR reported that this point was emphasised during closing arguments."Psychosis doesn't pop up when it's convenient," Assistant District Attorney Susan Caswell said. "That's not how mental illnesses work."Nolen had repeatedly tried to plead guilty and asked to be executed, but Cleveland County District Judge Lori Walkley declined to accept his plea. One of Nolen's attorneys had questioned whether his client was mentally competent to enter a guilty plea.A witness who testified during the trial said Hufford was "completely surprised" when Nolen came up behind her, pulled her head back and drew the knife across her throat. Gary Hazelrigg also told jurors that he screamed and cursed at Nolen during the attack and tried to pull him off Hufford."I was looking at something horrific — something that people shouldn't have to see," Hazelrigg said.At a 2016 hearing, Nolen told the judge that he would only accept a death sentence, not life in prison with or without the possibility of parole. The judge repeatedly reminded Nolen that if he pleaded guilty and waived his right to a jury trial, the decision to sentence him would be up to a judge, not him.