But he now runs a home in South Wales for young men whose lives have been disfigured by drink and drugs, where his hand is paternal but firm: smoking, drinking, dope and 'worldly conversation' are banned.
Mr Blajos is a star turn for Victory Outreach, the California- based Christian evangelist organisation to which he is now dedicated. So violent, so lurid is his background in Boyle Heights, eastern Los Angeles, that his conversion to Christianity - initiated, he says, by a fellow prisoner at the top of his hit-list - is broadcast by his church as one of the great miracles.
'Eight out of ten people I used to know have died,' Mr Blajos said. He pulled up the sleeve of his T-shirt to reveal, on the inside of his right arm, a tattooed black hand, the motif of the Mafia assassin. He knifed his first victim to death while in jail as a 16-year-old. 'After that, I looked in the mirror and saw something different. I lost the capacity to feel things.'
A member of the Mafia by the age of 19, Art spent 21 of his first 35 years in penal institutions, specialising in the assassination of fellow prisoners. He is a singular figure on the leafy Victorian streets of Penarth, and in Cardiff, where he tells the world through a megaphone of Jesus saving him from his past.
Mr Blajos, who is 42, has been in South Wales for six months. His missionary work for Victory Outreach began a few miles up the valleys in Treforest, based in the home of a fellow church member. The reaction was mixed.
'Some people thought we should go home. They'd say 'haven't you got enough crime in America?' ' The rehabilitation home in Penarth houses young men such as Greg, 31, a New Zealander with a background of drug abuse, Jeff, 21, an LSD taker, and David, 25, from Newport whose drink problem meant he could not hold down a job.
Anyone using the home as a doss-house is weeded out. When David began drinking again, his future there was uncertain. 'But Brother David was remorseful. Some people don't want to be worked with . . . they don't want to get up in the morning for prayers. I make the decision whether they stay or leave,' Mr Blajos said.
He said in Cardiff, he had been spat at and had rocks thrown at him. These may be trifles when compared with his earlier life of cocaine addiction and murder, yet South Wales can sometimes shock him. 'I couldn't get over all the young kids on the street here smoking fags. And alcoholism. There's a lot of that,' he said.
Even reborn, Mr Blajos looks almost a caricature of a gangster: moustachioed, hair swept back.
He remains disturbingly muscular. What if he is provoked? 'The temptation is there to do some great bodily damage. It is Jesus Christ in me that gives me grace,' he said.
As Mr Blajos and his team worked towards 'cracking' Cardiff city centre on a busy afternoon, he encountered a man only interested in the price of his megaphone and an indignant woman who demanded to know just what sort of a Christian he was. A young man with a beard said he would come to the Hotel Diplomat for one of Victory Outreach's Sunday gatherings. 'Last time I went it was for a psychic fair,' he said.
Mr Blajos and his team also target some of Cardiff's most deprived estates.
In the US his life has been re- enacted for a fundamentalist television series, Treasures out of Darkness. Child actors play Mr Blajos and his brother after they were abandoned by his parents. 'I'm the fat one,' he laughed. Later, we witness his conversion - Mr Blajos plays himself - recreated inside Wayside County Jail, Los Angeles.
He is shown reaching out to grasp the Bible belonging to the man he intended to kill. 'I prided myself on always carrying out a commitment . . . But for some reason I didn't want to drill this guy. I looked into his eyes and felt compassion.'
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