German Social System

The authorities have to (and do) investigate all cases impartially. For criminal cases (and that includes aggression and bodily harm), the investigation cannot be stopped by the accuser withdrawing his/her report. This is because investigating such cases further is seen as in the public interest, which the authorities must follow under all circumstances.
In addition, your friend was convicted in the end, despite his and his lawyers efforts. Thus, in the eyes of the law, he committed the offense, the investigation was justified and he is listed in the police database as criminal.
Then the authorities must ensure the safety of his wife and kids. After all, they don't know if he will do it again. Even if the wife does not (or not any more) dispute his custody for the children, the youth authority (Jugendamt) will continue to investigate and can remove his custody rights if they find this is in the best interest of the children (the wishes of the parents are secondary here!).
He can of course file for divorce, but usually one year of separation is required for a divorce to be granted. He can of course also search for another place to stay, if he wishes to.
Probably the best advice to him is to co-operate with the authorities to the full extent, follow all suggestions of his lawyer (I hope he has a good one) and prove (over a period of many months or years) that he has changed and such behaviour does not happen again. Then the restrictions might be removed and he can go on with a normal life - with or without his wife and children.

thanks a lot for your kind reply. I really appreciate your patience to have written about this to me in detail. 

If we both wish to get married to each other, then what should be the best course of action. He is currently having a criminal lawyer but his divorce lawyer although had drafted the divorce petition has not filed it in the court, maybe waiting for that 1 year to end?

However, meanwhile he is been rejected for house due to his criminal background and the name in the computer, he is still trying for the same.

He has been denied by the state for his wife's expenditure even if the state has already put him in a bracket for separated people. His wife who is now back with him under the same roof along with the kids is staying here and does not wishes to move to some other place although he is unable to find a house for himself.

Any good lawyer you could suggest and reply urgently will be of great help. He is living with her under constant threat that even lets say she hurts herself accidentally while doing house hold work, there are strong chances of him to face the repercussions and sentence.

Kindly help us with a strong advise and help with the details, will be indebted to you forever.

He can only re-marry (you) after a divorce.
A divorce without at least one year separation is possible only if both partners agree.
If he wants to divorce quicker, I suggest he finds an agreement that his wife accepts. Usually, this involves payment of quite a lot of money, or other benefits for her, on top of the lifelong maintenance payments his wife and kids will be entitled to in any case (unless she earns more than him).
It is very difficult for a convicted criminal to find housing in Germany. A background check is part of most tenancy agreements and most landlords wouldn't rent a flat to a violent criminal. He could stay in a hotel (if he has money) or a homeless shelter (if he has none).
If he is unhappy with his current criminal and divorce lawyer, he can check the yellow pages or search the Internet for others.

Sorry that I could not revert, as I was out of India, Thanks a lot for your reply once again.
Now the fact is that he does not have enough money to stay in the Hotel, and I really wonder if he is accused as a criminal how can he seek the shelter from the Government.
However, his wife is still staying with him under one roof and has backed out on her previous complaint of strangulation by him as mentioned before.
His lawyer suggested that it would be really advisable for him to move and stay away from her under these circumstances as any natural accident could be just alleged onto him and there are chances of severe repercussions. I do not know that since she has backed from her compliant if there are chances that she would settle on any amount of alimony.
With regards to his divorce his lawyer has not guided anything to him and has not filed anything in the court as he is on vacation.
His criminal lawyer had told him that he has contacted the court in Germany with some reply from their side to counter the criminal case and to not accept the term of 4 months that he has now been awarded, although he was told that his file is now being read by a new judge in the court and that he has no idea what comes next now as there could be any outcome and he should be prepared for that. His lawyer also says that it is a very complicated case and one of a kind and that his lawyer can not foresee anything now right now as to what can happen to my boyfriend. Kindly suggest a good criminal lawyer and suggest some remedies for us to get rid of this and get married to each other without much delay and problems. I will be indebted and grateful to you for your kind help and support.

Sorry, without knowing the exact details of his case (and without being a lawyer), I am unable to advise you further to what I wrote above.
He should definitely follow all advice from his lawyer(s)!
A conviction for a violent crime is very serious in Germany and will cause him many problems in future (not only when looking for accommodation). It is also very possible (he should ask his lawyer about this) that his visa for Germany will be revoked or not renewed because of this. So he might probably have to consider returning to India. (At least you two can then meet or live together easily while he's waiting for his divorce.)

Well he is a German citizen with German nationality with a German passport. However, thanx a lot for your precious replies Im really indebted

Oh, he is GERMAN?
Well, then he should know all these things better than me and is certainly also able to understand the situation, select and communicate well with his (German) lawyers.
In that case, I really don't know how to help you further.

But please don't put your hopes high for a speedy solution (unless he pays his wife enough so she agrees to a quick divorce). Disputed divorce cases can take very long (and he will most likely be a pauper afterwards)!
Getting a German visa through being married to him (in case that is what you have in mind) may not be possible for several years.

to tell u the truth he is an Indian Afghani with a german nationality for the last 20 years. His previous passport was issued in kandhar Afghanistan.

I could nt exactly understand.... what do you mean by this!!

What do you not understand?
I am happy to explain again.

I have applied for a job seeker visa for Germany. I truly love him, it is not for a nationality otherwise I would not even have dream't of getting married to a convict. I truly madly and deeply love him and that is the reason that I am with him through thick and thin.

What if I have a child out of wed lock from him then what are the repercussions, for now my boy friend is living there with his wife but if I can get a house he can stay with me. Well he is a middle class person does not really earn good, but is a good human being and that is what really matters to me. He can not pay his wife an handsome amount to get divorced from her..... Although we both wish this happens as soon as possible.....

Please suggest if I have a child from him out of wedlock???
any advise is more than welcome.

Under German law, it does not matter much if a kid's parents are married or not - as long as the father accepts legal fatherhood (an official statement to this effect is needed if the parents are not married) or is genetically shown to be the father.
In fact, there are about as many kids born out of wedlock as within in Germany nowadays.
But other countries (incl. India) may handle this very differently.
And you must always keep in mind that he will be obliged to pay maintenance for his current wife and children, possibly for life. A divorce also costs a lot, even if both sides agree this is several months salary!

thanx a lot beppi, I know I get it but I have had a bad relationship as well, he is trying that his wife should be convinced that he can not stay with her anymore but it seems that he is under pressure due to the conviction announced in the court. by the way if he pays for them I mean his wife and kids life long is really not a problem to me as I am not with him for money or any other thing but just for love and happy companionship!!!
I would really want to have it sorted as soon as possible if not then I have no other option but to have a child out of wedlock from him if it does not harm his criminal case as such!!
I am presently working with LH as a regional flight attendant, employed for 12 years with them, have been flying for the last 15 years, fly from India to germany and have layovers in germany and that is where I met him and got to know him. he is doing everything what is lawyer is saying but the conviction for 4 months is a great problem, we both want to avoid it so that we can have a better future together.
he is a teamlieter by an speiliotheck and has done his schooling from hamburg.
I have also passed a german B1 test through Max muller bhawan delhi, after my graduation in delhi.
Currently applying for a job seeker visa hope I can succeed in that and try to live with him hopefully if not married to him at least can have a family with him, although my family in india will never approve of it and will cut all the ties with me for this I just hope that I don't need their help ever in my life and can sustain my child as long as he is with me.

I will be really indebted if you can help me with this One..... Since his Lawyer is presently on vacations he has not yet Filed The divorce in The Court.... What if he becomes a Muslim and Marries me legally... Do u think that this will be a better Option than having a Child Out of wedlock.... Any Advise will be appreciated Thanx a lot.....