Mr Estermann was killed soon after he was appointed commandant of the guard

After a nine-month inquiry, it upheld its preliminary finding that Alois Estermann and his wife, Gladys Meza Romero, were killed by Swiss Guard Corporal, Cedric Tornay, who then turned the gun on himself.

The Vatican said the 23-year-old recruit acted in a fit of madness after his newly-appointed commander refused to give him a military decoration.

It dismissed the possibility of other suspects and said the were no grounds for conspiracy theories.

The Vatican said it had found traces of cannabis in Tornay's body and could not rule out that he may have been a chronic drug user, which "would further explain his behaviour".

Gladys Meza Romero: Was also killed

It said an autopsy had also found a cyst the size of a pigeon's egg in Tornay's brain.

"The Estermanns were killed by Vice Corporal Cedric Tornay, who immediately took his own life with the same service revolver," the report concluded.

But Tornay's mother has accused the Vatican of covering up the truth and said she had documents to prove her son's innocence.

"The official version is full of deceit, contradictions and lies which hide a probably inadmissable truth," she told Il Messagero newspaper.

Vatican spokesman Joaquim Navarro Valls maintained that the investigation had been thorough.

Mr Estermann shielded the Pope during an assassination attempt

He said: "Her sorrow is understandable and must be respected, but must be consistent with the most scrupulous respect of truth as it has been established.

"Tornay killed the others and then committed suicide, that's the result of a long investigation."

The elite Swiss Guard helps to protect the Pope and stands guard at official ceremonies.