A 19-year-old who officials say illegally entered the U.S. in 2022 pleaded guilty Wednesday in Harford County Circuit Court to first-degree murder in the strangulation death of Kayla Hamilton, a 20-year-old Aberdeen woman with high functioning autism.

Walter Javier Martinez was 17 when he was arrested and charged with first- and second-degree murder, first- and second-degree rape, a third-degree sex offense, robbery, assault and theft. Judge Yolanda L. Curtin sentenced him to life in prison with all but 70 years suspended.

According to a news release from the Harford County State’s Attorney’s Office, Martinez illegally entered the U.S. from El Salvador in March 2022. His defense team stated during the trial that Martinez employed “cayotes” — people who are paid to move things illegally across the border — to get him into the country when he was 16 years old and that he is a member of the gang MS-13, according to the news release.

Hamilton and her boyfriend moved to the 100 block of East Inca Street in Aberdeen from Virginia several months prior to her death. Martinez had been staying at the home for five days prior to the murder, according to the news release.

On the day of her murder, July 27, 2022, Hamilton was alone in the home with Martinez for the first time. Hamilton called her boyfriend when someone knocked on the door of their bedroom and the murder was recorded on a voicemail which was played in court in support of Martinez’s plea, according to the news release; on the recording Martinez could be heard apologizing to the victim.

Hamilton’s body was discovered by her boyfriend, who said he saw Martinez walking down the street away from the residence shortly before he arrived at the scene. Hamilton’s body was bound at the wrists with a phone charger tightly wrapped around her neck and her mouth, according to the news release.

The Office of the Chief Medical Examiner ruled the death a homicide by strangulation.

DNA taken from Hamilton’s body and clothing connected Martinez to the scene, according to the news release.

After Martinez was arrested, he wrote a letter from the Harford County Detention Center in which he admitted to committing four murders, two rapes and additional crimes, according to the news release.

“This defendant, residing in our country illegally, had no legal right to be here, preying on the members of our communities, and perpetuating the same violent gang activity that he did in his own country,” Harford County State’s Attorney Alison Healy said in the news release. “This murder was one of the most brutal and heinous crimes I have ever prosecuted.”

Healy stated that the state could not seek a sentence of life without parole because Martinez was only 16 at the time of the murder. In addition, Healy said Martinez may be subject to additional immigration proceedings and deportation after his release from prison, as an Immigration and Customs Enforcement detainer would be in effect.