I found a large amount of money in my account twelve years ago, and I was in need of it, so I spent it. I do not know who deposited it in my account. We checked with the bank and they could not find the name of the person who deposited it. All they were able to find out was the place where the deposit was made. Now I want to discharge my responsibility concerning it. Should I give the money to some charitable cause, with the intention of the reward going to the person who deposited the money in my account?

Praise
be to Allah

The depositing of the money in your account may have been a
mistake, or it may have been done deliberately. But the idea of it having
been done deliberately is very unlikely, because in that case it would be
money that the owner did not want, and he gave it to you, so you could keep
it. If it was done by mistake – which is what appears to be the case – then
it must be returned to its owner. If you are not able to find out who its
owner is, then you should give it in charity on his behalf, on the basis
that, if one day you find out who its owner was, you will give him the
choice between approving of that charity or taking back his money. 

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him)
said:

If a person has money or property, and does not know who the
owner is – as in the case of one who seized it by force and has repented, or
one who acquired it by treachery and has repented, and the like, who has
property in his possession of which he is not the owner, but he does not
know who the owner is – then he should give it to people who are in need or
spend it in the interests of the Muslims. 


Al-Fataawa al-Kubra
(4/220) 

He (may Allah have mercy on him) was also asked about some
pilgrims who encountered some Bedouin bandits who had been raiding
travellers and had taken their fabric. They fled, leaving behind their
camels and the fabric. Is it permissible to take the camels that belonged to
the thieves and the fabric that they stole, or not? 

He replied:

Praise be to Allah. What they took of the pilgrims’ property
must be returned to them, if possible. This is like lost property which
should be announced for a year. If its owner comes along and claims it, all
well and good, otherwise the finder may spend it (or use it) on condition
that he assume liability. 

But if the finder despairs of ever finding its owner, then he
may give it in charity and spend it in the interests of the Muslims. 

The same applies to any property of which the owner is not
known, such as property seized by force, borrowed items, items that were
left in trust, and items seized from thieves, which belong to people, or
items that have been thrown away. All such property may be given in charity
or spent in the interests of the Muslims. 


Majmoo‘ al-Fataawa
(30/413) 

And Allah knows best.