First of all leather in cars may not be najis. You have to know for sure that it is from a najis or animal that is slaughter in a non halal way to consider it najis. If you do not know that you consider it pure.
If you know for sure that it is najis, then their jacket has also become najis.
If it is najis then it will make a second item it touches najis if it is moist. If there is reason to believe that the jacket has been washed… which is most likely the case, or it got rained on and purified; you can consider it pure.