How to check past years it return status?

the thing is, my friend got a notice that his return was filed in 2006-07, but he had not filed his return, in fact he had never filed his return ever till last year... He is into his father's business and last year he started business of his own, before which he was working for his father only... now as he filed his return this year, he got a call from the IT department claiming that his return was previously filed in 2006-07 :X we now have no idea as to what has happened as my friend has never filed his return. Can you help me in letting me know as to how can we check whether the return was ever filed or no how can we check that?? please help asap