I'm so impressed with Thera Nagasena's answers. By the way Heinous Crimes :
killing one’s mother, one’s father, an arahant, drawing blood from a
Tathàgata or violating a nun (the Sinhalese also gives damaging a bodhi tree). One
guilty of these offences should not be ordained. If they are ordained they should be
King Milinda and Thera Nagasena
THE LAYMAN'S SIN.
[The Questions Of King Milinda,Translated by T.W.Rhys Davids]
King:  'Venerable Nâgasena, suppose a layman had been guilty of'Heinous Crimes', and some time after should enter the Order. And neither he himself should be aware that when still a layman he had so been guilty, nor should any one else inform him, saying: "When a layman you were guilty of such an offence." Now if he were to devote himself to the attainment of Arahatship 2, would he be able so to comprehend the Truth as to succeed in entering upon the Excellent Way?'
Nagasena: 'No, O king, he would not.'
King: 'But why not, Sir?'
Nagasena: 'That, in him, which might have been the cause of his grasping the Truth has been, in him, destroyed. No comprehension can therefore take place.'
King: 'Venerable Nâgasena, your people say:
"To him who is aware (of an offence) there comes
remorse. When remorse has arisen there is an obstruction in the heart. To him whose heart is obstructed there is no comprehension of the Truth 1."
'Why should there then be no such comprehension to one not aware of his offence, feeling no remorse, remaining with a quiet heart. This dilemma touches on two irreconcilable statements. Think well before you solve it.'
Nagasena: 'Would selected seed 2, O king, successfully sown in a well-ploughed, well-watered, fertile soil, come to maturity?'
King: 'Certainly, Sir!'
Nagasena: 'But would the same seed grow on the surface of a thick slab of rock?'
King:'Of course not.'
Nagasena:'Why then should the same seed grow in the mud, and not on the rock?'
King: 'Because on the rock the cause for its growth does not exist. Seeds cannot grow without a cause.'
Nagasena: 'Just so, O king, the cause by reason of which his comprehension of the Truth (his conversion) might have been brought about, has been rooted out in him. Conversion cannot take place without a cause.'
King: '[Give me, Sir, another simile 3.']
Nagasena:'Well, O king, will sticks and clods and cudgels 4
and clubs find a resting-place in the air, in the same way as they do on the ground?'
King: 'No, Sir.'
Nagasena:'But what is the reason why they come to rest on the earth, when they will not stand in the air?'
King:'There is no cause in the air for their stability, and without a cause they will  not stand.'
Nagasena: 'Just so, O king, by that fault of his the cause for his conversion has been removed. And without a cause there can be no conversion. Now will fire, O king, burn in water in the same way as it will on land?'
Nagasena: 'But why not?'
King: 'Because in water the conditions precedent for burning do not exist. And there can be no burning without them.'
Nagasena: 'Just so, O king, are the conditions precedent to conversion destroyed in him by that offence of his. And when the conditions which would bring it about are destroyed there can be no conversion.'
King: 'Venerable Nâgasena, think over this matter once more. I am not yet convinced about it. Persuade me by some reason how such obstruction can occur in the case of one not aware of his offence, and feeling therefore no remorse.'
Nagasena: 'Would the Halâhala 1 poison, O king, if eaten by
a man who did not know he had eaten it, take away his life?'
King: 'Yes, Sir.'
Nagasena:'Just so, O king, is there an obstruction to his comprehension of the Truth, who, without being aware of it, has committed a sin. And would fire, O king, burn a man who walked into it unawares?'
King: 'Yes, Sir.'
Nagasena:'Well, just so in the case you put. Or would a venomous snake, if it bit a man without his knowing it, kill him?'
King: 'Yes, Sir.'
Nagasena:'Well, just so in the case you put. And is it not true that Samana Kolañña, the king of Kalinga,--when surrounded by the seven treasures of a sovereign overlord he went mounted on his state elephant to pay a visit to his relatives,--was not able to pass the Tree of Wisdom, though he was not aware that it was there 1? Well, of the same kind is the reason why one who has committed an offence, even though he know it not, is nevertheless incapable of rising to the knowledge of the Truth.'
King: 'Verily, Nâgasena, this must be the word of the Conqueror. To find any fault with it were vain. And this (explanation of yours) must be the meaning of it. I accept it as you say.'
Love Buddha's dhamma