Prisoner tried to carve '666' into his forehead - but used a mirror so it came out backwards [PHOTOS]

Convicted killer Nikko Jenkins, 28, pictured above in 2014, recently tried to carve the sign of the beast '666' into his forehead but he used a mirror so the numbers came out backwards. Now he has a series of upside-down 9s across his face, this is according to what he told his lawyer.

It is believed that Jenkins, who is currently appealing his death penalty, may use the botched case of self-mutilation as evidence that he's mentally unstable & therefore ineligible to face the death penalty.

Jenkins was convicted of shooting dead four people in 10 days after he was released from prison in Omaha, Nebraska, in 2013.

During his murder trial in 2014, the killer was assessed by a doctor who concluded that he was 'a psychopath' and 'one of the most dangerous people' he had ever encountered.

Jenkins first pleaded not guilty for the murders, then pleaded guilty, then changed his mind and said he was ineligible for trial on the grounds of insanity. The court will decide whether to sentence him to death or not in July.