Unleavened bread shall not be found in the possession of a Jew
“for seven days’ leaven shall not be found in your houses” Shemos 12;19
If one places leaven in his house on Pesach, for example he lets dough become leaven on Pesach and leaves it in his home or he buys leaven bread and stores it wilfully he should receive two lashings due to these actions. ( -2 and –3).
However, if leaven bread remains in his house from before Pesach and has not been destroyed he violates 2 prohibitions as above but does not receive a whipping as he has done no physical actions.
Bread of non-Jews that is found in the possession of a Jew where the Jew has the responsibility to look after it, must be destroyed.
However, if he has not accepted this responsibility there is no prohibition to keep it.
As it says in Shemos 13;7 “Yours shall not be seen” what is yours shall not be seen however you may see that of others.
If the non-Jew could sue the Jew in the non-Jewish courts even though he did not accept any responsibility, then he must destroy it.
According to the Scribes it is forbidden to have any benefit from Chometz that has remained with him throughout Pesach as a penalty for transgressing- not being seen (-2) and not being found (-3)
Even if forgotten inadvertently it is prohibited to him.
This applies in all places at all times for man and women.