Mishnah Berurah — משנה ברורה

Stolen ones - For it's considered a mitzvah that came through a transgression. And even after the owner despaired [of ever recovering it], and even after the fact, [the one who used it] did not fulfill the mitzvah of tefillin. However, if one sold the tefillin after the owner despaired, the opinion of the Magen Avraham in siman 449 and the ??? above in siman 11, is that the second one (ie. the buyer) is allowed to recite the blessing on them, because for him the despair was effective and there was a change in possession [of the stolen item]. However, the Ta"z and the Gr"a in this siman wrote explicitly that it's forbidden to recite a blessing [on them] no matter what. But regarding whether one can fulfill the mitzvah with them, it's seems from the Gr"a that one would fulfill the mitzvah with them. But regarding the blessing, it's forbidden because of [that which is written: “The robber who recites a blessing [blasphemes the Lord]” (Psalms 10:3). For through his acquiring it, the stolen item went out from the possesion of the owner. However, one who acquires it from the second one (ie. from the buyer), it seems that he would be able to recite the blessing on them, that is what I found written in Damasek Eliezer above in siman 11, see there further.