Alastair Graham was looking after Bruno, a Staffordshire Bull Terrier cross, for a friend when he snapped after the animal bit his finger.
He tied the animal to a tree in Kirkcaldy’s Dunniker Woods and initially attempted to slit its throat and stab it to death.
But when he failed Graham went to a nearby petrol station and filled up a jerry can before pouring it over the terrified dog.
He then set the dog alight - causing horrific full thickness burns to the defenceless animal.
A sheriff told Graham the attack was a “grotesque act of savagery”.
But the Animal Health and Welfare Act that he was prosecuted under means Graham can only be jailed for a maximum of a year.
However he will face “years” in jail after he also admitted an attempted knife robbery carried out days after he killed Bruno.
Fiscal depute Susan Dickson told Kirkcaldy Sheriff Court that a post-mortem on Bruno revealed he had still been alive when Graham had set him alight.
She said: “Around 2pm on April 25 a dog walker saw a black object around 10 metres from a path - he looked more closely and saw it was the remains of a dog.
“Police attended and the area was secured - attempts were made to see if the dog was microchipped but it was not.
“It’s owners could not at that time be found but information as to its owner was later received.
“On April 28 the owner met Mr Graham and brought the story about the dog being found up on the TV.
“The accused initially said ‘that’s sick’.
“They went into the kitchen and Mr Graham then said ‘it was me’.
“Mr Graham had been looking after the dog for the owner as a favour.
“The owner asked why he hadn’t brought the dog back and Graham said he hadn’t thought about that.
“He said the dog had been biting him and he snapped - he said he didn’t want it biting anyone else.
“He said he had tried to cut an artery but it didn’t work.
“Later the police made officers aware of the admissions Mr Graham had made.
“Footage from the BP petrol station showed the accused filling up a container with petrol on the day in question - a similar container was found melted beside the dog.
“A post mortem on the dog was carried out which revealed the burning was concentrated over the neck, head and thorax areas with the right side badly burnt to full thickness.
“There was a thick black deposit round the neck consistent with the harness - the metal parts were burnt on to the neck.
“There was inhalation of smoke in the dog’s airways which indicates it was alive when it was set on fire.
“There was also a deep sharp puncture would and another sharp wound - neither of which were life threatening but would have caused pain.
“The accused when interviewed said he had taken the dog for a walk but it had run away.
“He later admitted his actions.”
Graham, 23, a prisoner at HMP Perth, pleaded guilty on indictment to causing Bruno unnecessary sufering by causing his death in the fire on April 24 or 25.
He further admitted an attempted knife robbery committed alongside Steven Gourdie, committed on May 2 at High Street, Leven.
Larry Flynn, defending Graham, said: “He has a vague recollection of doing this but was abusing alcohol at the time.
“His recollection is that he attempted to kill it with a knife but he failed and he went to get the petrol then returned.”
Sheriff James Williamson deferred sentence on Graham and Gourdie until next month for social work reports and a risk assessment.
He said: “He went about this in a calculated manner - it wasn’t a spur of the moment thing.
“This was a grotesque act of savagery.
PC Ian Laing, Wildlife Crime Officer for Police Scotland’s Fife Division said: “This defenceless animal suffered immensely prior to its death and the incident evoked considerable outrage from the local community.
“A robust investigation was launched to identify whoever was responsible, resulting in Alastair Graham being arrested and charged.
“His guilty plea is testament to the work carried out by Police Scotland to bring this offence to trial and the support from the public who provided vital information during our enquiries.”