The Halacha requires one to own the Masa used to fulfill the Misva on the Seder night. The Hachamim derived this from a Gezerah Shavah between the Pasuk dealing with separating Halla- “Reshit Arisotechem” (YOUR first dough) and the Pasuk describing Masa as “Hallat Masa.” Just as one must own the dough in order to separate Halla, so too he must own his Masa. Accordingly, stolen Masa may not be used for the Misva, as it does not belong to him.
Nevertheless, the Shulhan Aruch at the end of Siman 454, rules that if the stolen Masa underwent a Shinui (change), the thief then acquires the stolen Masa, and merely has to repay monetary compensation and not return the original item. The Gemara brings the example of one who stole wheat and then ground it to make flour. He fulfils his obligation with Masa made from that flour since it underwent a Shinui Ma’aseh-a physical transformation. That is, it is no longer the same object he stole. However, he does not recite the Beracha on such Masa, since, as the Gemara says, it is not a blessing but “Mina’es”-despicable.
The Be’ur Halacha brings the question of Rabbi Akiva Eger, based on the RItva: Every time one eats stolen Masa, he first chews it before swallowing. Shouldn’t that change in consistency constitute a Shinui Ma’aseh, enabling the thief to gain ownership of the Masa before he fulfils the Misva by swallowing? He answers that, indeed, according to the RItva, he does fulfil the Misva with stolen Masa. Although the Shulhan Aruch does not rule in accordance with this opinion, and he must eat another piece of Masa which he legitimately owns, it does carry enough weight to create a “Safek Berachot,” so that he should not make a new Beracha on the second Masa.
The Be’ur Halacha also cites the Machloket between the Poskim whether this Halacha requiring ownership of Masa also applies to the Maror. Some Poskim hold that it does not, and one fulfils the Misva with stolen Maror. Others hold that Maror is equated to the Masa in the Pasuk, and it also must be legitimately owned. The Be’ur Halacha asks, according to the opinion that there is no requirement to own the Maror, still, how he can fulfil the Misva with stolen Maror. Doesn’t eating stolen Maror constitute a Misva Haba’ah Ba’Averah-a Misva performed via a transgression, which is invalid? He answers, based on Maran’s ruling in Hilchot Lulav. There Maran rules that on the subsequent days of Succot one fulfils the Misva using a stolen Lulav, since after the first day there is no longer a requirement for ownership, and it is not a Misva Haba’ah Ba’averah, since it is only a Misva M’drabanan. So too, Maror is only a Rabbinic Misva and is not subject to the restriction of Misva Habah Ba’Averah.