Christa Pike, killer of her 18-year-old classmate in 1995, remained conscious and was snoring loudly despite receiving two doses of lethal injections Wednesday night, in a botched attempt by prison officials to carry out her death sentence.

Ms Pike, 50, was taken to a hospital after surviving two syringes of pentobarbital administered to kill her. Instead, her heartbeat remained intact while she snored audibly, according to reporters who witnessed the scene. They also said Ms Pike began to sing alongside her spiritual adviser at one point.

“I’m going to leave this world the way I spent most of my life,” Ms Pike said. “And that is with love.”

According to The New York Times, witnesses said Ms Pike described a burning sensation in her arm and asked if it was expected.

But over an hour later, witnesses said they could hear Ms Pike breathing and snoring loudly behind the curtain that demarcated the inmate on the gurney from the witnesses’ section.

Ms Pike’s lawyers had earlier warned that the execution by lethal injection could be more torturous for her than necessary, arguing she has small veins.

“We take no pleasure in being right, but the concerns raised by Ms Pike proved to be true: difficult vein access, blown veins, degraded pentobarbital, no emergency medical care available when things inevitably go wrong, all under a protocol that remains veiled in secrecy,” her lawyers said in a joint statement after the botched execution attempt.

The Tennessee Department of Correction insisted it “had followed every step of the state’s lawful, established execution protocol approved by the attorney general’s office”, adding that “the lethal injection chemical in the protocol has consistently been effective.”

Ms Pike murdered her classmate Colleen Slemmer, 19, in January 1995, whom she lured into the forest.

Ms Pike’s boyfriend, Tadaryl Shipp, and another friend pelted Ms Slemmer with asphalt rocks before slashing her body with a box carver. Ms Pike, 18 at the time, kept Ms Slemmer’s skull to brag to at least one person.

Mr Shipp testified that he carved a pentagram on Ms Slemmer’s chest, sparking fears of Satanism.

Ms Slemmer’s family, including her mother, May Martinez, insisted on Ms Pike’s execution, saying nothing else could atone for her daughter’s death.

Ms Pike said she felt remorse for her actions, and co-inmates described her as supportive and kind. She was diagnosed with bipolar disorder and post-traumatic stress disorder in prison, where she also received treatment.