How to purify a dead body that has been torn apart
Question

How can we purify the body of a dead person whose body was torn apart as a result of a car accident?
Praise be to Allah.If someone died as a result of a car accident and his limbs have been cut to pieces, then if possible they should all be washed, by putting his limbs together and washing all of them, because washing the dead is obligatory and it is possible in that case. But if it is not possible to wash all the parts, then whatever can be washed must be washed, and tayammum must be done for the rest.
An-Nawawi (may Allah have mercy on him) said: Our companions said: If it is not possible to wash the deceased because no water is available or he has been burned to the extent that if he is washed he will disintegrate, then he should not be washed: rather tayammum must be done, and this tayammum is obligatory, because it is purification that does not have to do with removal of impurity. So when it is not possible to use water, we must move to the option of tayammum, as in the case of ghusl for janaabah. Ibn al-Mundhir narrated from ath-Thawri and Maalik that when there is the fear that the flesh of the deceased will disintegrate if he is washed, and they will not be able to wash him, then water should be poured over him. According to Ahmad and Ishaaq, tayammum must be done. He [Ibn al-Mundhir] said: And that is also my view." (Sharh al-Muhadhdhab 5/140).
Ibn Qudaamah (may Allah have mercy on him) said:
In the case of one who died of smallpox, was burned to death or drowned, if it is possible to wash him then he must be washed. But if there is the fear that his body will disintegrate if water is used, then he should not be washed, and tayammum should be done instead, if possible, as in the case of a living person who will be harmed by using water. If it is not possible to wash the deceased because water is not available, tayammum must be done instead, and if it is not possible to wash some parts but it is possible to wash others, then that which can be washed must be washed, and tayammum must be done for the rest, just as in the case of one who is living." (Al-Mughni 2/210).
Shaykh Ibn Baaz (may Allah have mercy on him) was asked:
How should we wash a person if he died in an accident and his body was disfigured, and some parts may be cut off?
He replied: He must be washed, like anyone else, if that is possible. If it is not possible, then tayammum must be done for him, because tayammum takes the place of washing with water when using water is not possible." (Majmoo‘ al-Fataawa  13/123).
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked:
I came across a naked, dead infant in a stream; this infant was a newborn, and his body was disintegrating, so I could not wash him like the dead are washed, in accordance with Islamic teachings. Is there any sin on me for burying him without washing him, and what should I do if such a thing happens again?
He replied: If washing the deceased is not possible, then the scholars say that tayammum must be done, meaning that the living person should strike the dust with his hands, then pass them over the face and hands of the deceased, then he should shroud him, offer the funeral prayer for him, and bury him." (Majmoo‘ Fataawa Ibn ‘Uthaymeen  13/123).
And Allah knows best.