report claims ivan milat shot first victim years before backpacker murders .
the ` wrong man ' jailed for attack , which left milat free to kill , report says .
milat 's brother , boris , says he has kept the shocking secret for 52 years .
report claims milat shot and paralysed neville knight in march , 1962 .
` ivan shot him - he told me the next day , ' mr bilat said of the shooting .
milat brutally murdered seven backpackers between 1989 and 1992 .
he is serving seven consecutive life sentences at goulburn supermax jail .