A Fort Carson soldier told police he had "rough sex" with a 19-year-old woman and then slit her throat, leaving her to die in the forest west of Colorado Springs, according to an arrest affidavit obtained by 7NEWS.The coroner determined her cause of death as an "incised wound to the neck," the sheriff's department said Wednesday.Robert Hull Marko, 21, is being held without bond on suspicion of first-degree murder and sexual assault with a deadly weapon after police said he led them to the area of Old Stage Road where the naked body of Judilianna "Judi" Lawrence was found Monday.Authorities had been searching for the 19-year-old woman since she was reported missing by her mother last Friday.E-mails on Lawrence's computer led investigators to a MySpace page where a profile by "Rex290" was found. Photos on the page showed a soldier and investigators observed the name MARKO on the uniform. They contacted military police at the Fort Carson Army Base and asked for information on a soldier with the last name of Marko. Military police gave them information on Robert Marko.Investigators began questioning Marko Friday evening and he relented on Monday -- his 21st birthday, the El Paso County Sheriff's Office said. Marko said he met the victim on myspace.com and they met in person for the first time Friday.That's when Marko said he picked her up, took her to the woods for sex and then had an argument. According to the affidavit, Marko said he blindfolded Lawrence and gagged her before cutting her throat as she stood next to a tree.A person using his e-mail address advertised on a sex site for a "slave" partner who liked pain. On his MySpace page, Marko's profile said he could "kill without mercy or reason."According to the arrest affidavit, Marko admitted killing Lawrence when he was confronted with a bloody shirt found in his Army barracks at Fort Carson.Marko said that after he cut her throat, Lawrence managed to free herself and stagger away, the affidavit said. Marko told investigators that he found Lawrence walking down the hill and he ordered her to come back. The affidavit said that Marko admitted hiding the blindfold and gag in a nearby ravine.Investigators, using a map that Marko had drawn, found a pool of dried blood at the base of a tree in the area, according to the affidavit.Lawrence was reported missing after she failed to show up at S.A. Wilson special education school, where she attended classes for a learning disability.Marko has no shortage of younger female friends. A 17-year-old female friend posted on Marko's MySpace page, "How could u do this Robert, I loved and cared about u so much and all this news is breaking my heart and its tearing me apart I loved u and cared about u but now I'm so confused and heartbroken that I don't know what 2 think anymore."A 16-year-old female friend posted, "i love you no matter what and always will no one can change that i will come and see you i promise if they will let me i love you baby."Marko is a mortarman in the the 4th Brigade Combat Team of the 4th Infantry Division at Fort Carson in Colorado Springs. The unit suffered the highest casualties of any Army unit assigned to Fort Carson during its tours in Iraq. He is the sixth soldier from the unit to be suspected or convicted of killing someone after returning from Iraq.All 3,600 soldiers in the brigade have been screened twice for mental health and medical issues since returning from the war, and at-risk soldiers are due to be re-screened at the end of October.Sources at Fort Carson told the Colorado Springs Gazette that Marko received counseling for "an over-active imagination" after irregularities were found during a mental health screening in February, when his unit returned from Iraq. Marko received counseling and returned to duty, the sources told the newspaper.