The police forced him to divorce his wife with a threefold talaaq

Firstly: 

If a man is forced to issue a divorce by means of physical
harm or damage to his property, or threats to do such things to him or he is
threatened with imprisonment, by a person with power who he thinks most
likely will carry out his threat, the divorce does not count as such in that
case. 

It says in Zaad al-Mustaqni‘: Whoever is forced to do
something unjustly by means of harm caused to him or to his child, or by
having property taken away from him, or by means of threats to do one of
these things by a person with power who he thinks can carry out the threat,
and he issues a divorce on that basis, it does not count as a divorce. End
quote. 

Ibn al-Qayyim (may Allah have mercy on him) said: The
Sahaabah ruled that the divorce issued by one who is forced to do it does
not count as such. It was narrated from ‘Umar that a man suspended a rope so
that he could collect honey from the mountain; his wife came to him and
said: I shall certainly cut the rope if you do not divorce me. He adjured
her by Allah not to do that, but she insisted, so he divorced her. He came
to ‘Umar and told him what had happened, and he said to him: Go back to your
wife, for this is not a divorce. The opinion that it does not count as a
divorce was also narrated from ‘Ali, Ibn ‘Umar and Ibn al-Zubayr (may Allah
be pleased with them).

End quote from Zaad al-Ma‘aad, 5/208 

And he (may Allah have mercy on him) said: He [i.e., Imam
Ahmad] said according to the report of Abu’l-Haarith: If one who is forced
issues a divorce, the divorce is not binding. If something similar is done
to him as was done to Thaabit ibn al-Ahnaf, then he has been forced, because
they squeezed Thaabit’s leg until he issued a divorce. Then he went to Ibn
‘Umar and Ibn al-Zubayr, who did not think it counted for anything. And
Allah, may He be exalted, says (interpretation of the meaning): “except
him who is forced thereto and whose heart is at rest with Faith”
[al-Nahl 16:106]. This verse was quoted as evidence by Imam al-Shaafa‘i
(may Allah have mercy on him) to prove that divorce issued by one who is
forced does not count as such. 

In Sunan Ibn Maajah it is narrated from Ibn ‘Abbaas
(may Allah be pleased with him) that the Prophet (blessings and peace of
Allah be upon him) said: “Allah has let my ummah off for mistakes,
forgetfulness and what they are forced to do.

End quote from I‘laam al-Muwaqqi‘een, 4/51. 

Based on that, your divorce does not count as such and your
wife is still married to you. 

You have to refer your case to the shar‘i court to cancel the
divorce and take back your property. 

Secondly: 

The threefold talaaq counts as one talaaq according to the
correct scholarly view. So whoever divorces his wife with a threefold talaaq
– willingly – it counts as one talaaq and it is permissible for him to take
her back during the ‘iddah. 

Thirdly: 

If the wife knows that her husband’s talaaq was issued under
duress, it is not permissible for her to marry another husband, because she
is still married to the first one; her second marriage is invalid and it is
zina (adultery). 

And Allah knows best.