WARNING: DISTURBING CONTENT: Luis Gustavo Aroyo-Lopez, 24, was sentenced to life in prison for the murder and decapitation of his 64-year-old grandmother, Elvia Lopez-Aroyo

A man from California has earned himself a stretch of at least 25 years behind bars for the chilling crime of murdering and beheading his own grandmother, before heartlessly disposing of her head by a creek.

Luis Gustavo Aroyo-Lopez, 24, with a prominent "420" tattoo emblazoned on his forehead, pleaded guilty to the grisly murder last month following the death of 64-year-old Elvia Lopez-Aroyo. The judge slapped him with a life sentence eligible for parole after 25 years, tossing in an extra seven years for assaulting a guard while locked up, court records revealed.

In court on Thursday, relatives denounced the murderer, calling out his pretence as a "gangsta" when he is nothing but an absolute "coward," according to the Press Democrat. Gabriela Mejia, the victim's daughter-in-law, voiced the family's profound grief, saying, "What he did has left the family very hurt," adding: "We ask for justice because what he did was inhumane."

An apology was read out by Aroyo-Lopez's lawyer during the sentencing, with Aroyo-Lopez expressing he was sorry for "all the pain I caused you." Lawyer Nate Raff echoed his client's sentiments, admitting, "What I did was unforgivable."

On the afternoon of November 2 at around 3.40 pm Santa Rosa Police Department officials were summoned to the 2500 block of Pomo Trail where they stumbled upon the gruesome sight of decapitated Lopez-Aroyo sans head. It was later confirmed that Aroyo-Lopez had conducted a "targeted attack before leaving with the female victim's head," according to a chilling press release.

At the crime scene, police came upon numerous weapons, though the motive behind this gruesome act remains a mystery. Cooperating with the US Marshals Service, detectives spread the word about Aroyo-Lopez to fellow law enforcement in hopes of catching him.

Their efforts paid off on November 4 when an "alert" San Francisco Police Department patrol officer spotted Aroyo-Lopez at the Transbay Transit Centre, identifying him by his standout tattoo, a sizeable "420" with a marijuana leaf on his head that he'd seen in a wanted persons bulletin.

The officer apprehended Aroyo-Lopez effortlessly. Santa Rosa police detectives then journeyed around 60 miles to San Francisco to take him back to be detained at the Sonoma County Main Adult Detention Facility.

While Aroyo-Lopez was securely held, officers faced the grim responsibility of finding his grandmother's severed head. Success came at approximately 7.30 pm on November 4 when they located it on the south bank of the Santa Rosa Creek, a mere half-mile from where her life was cruelly taken.

Her head has since been transported to the medical examiner's office for examination, and while the cause of death is yet to be released, the savage slaying has dealt a devastating blow to the victim's family. "She was a loving person and she adored so dearly all her grandchildren. She didn't deserve what was done to her. Her death has impacted our family greatly and we are seeking for help during this time of despair," read a statement on a GoFundMe fundraiser set up in her memory.

Aroyo-Lopez had only recently been released from prison following previous convictions for assault with a deadly weapon and weapons possession charges not connected to the slain victim. A neighbour, only identified as "Jessica" citing worries over personal security, told KPIX, a CBS affiliate in San Francisco, about her observations leading up to the gruesome killing.

Jessica vividly recounted to the news channel her sighting of Aroyo-Lopez ambling towards the ill-fated woman's abode on that fateful November 1 afternoon. "He just walked a normal pace and, made an exact turn up the walkway, and knocked on the door. I paused over here with my dog just to make sure my neighbour knew who he was," said the vigilant neighbour.

Adding to the chilling narrative, Jessica disclosed to the broadcaster: "[The victim] was surprised and happy, and I heard the word 'you.' They were just, you know, talking and then the door closed, and I thought, 'Phew! She knows the guy.'".

"She was a loving person and she adored so dearly all her grandchildren. She didn't deserve what was done to her. Her death has impacted our family greatly and we are seeking for help during this time of despair,".

Jessica described hearing a woman emerge from the house about three hours after spotting Aroyo-Lopez, frantically shouting about a gruesome discovery. "She kept yelling 'No head! ' and I wasn't sure what she meant," Jessica revealed, adding that the horrified woman seemed to be desperately searching the property. According to The Press Democrat, the woman who made the horrifying discovery was the victim's own sister.