All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
In principle, all kinds of food are lawful except meat, as it [meat] is in principle forbidden until proven lawful. Therefore, if a Muslim doubts any meat whether or not it is pork (or contains pork), then it is not permissible for him to eat, until he ascertains it is not pork and does not contain pork.
Food - other than meat - is in principle lawful. Therefore, it is permissible for a Muslim to eat any food he wants, as long as as he is sure that it is forbidden, and mere doubt does not render the food forbidden.
There are two conditions for slaughtering tamed animals:
According to some scholars it is also desirable to cut off the two jugular veins. On the other hand, some other scholars it is a condition to cut off all these (i.e. the throat, the gullet, and the two jugular veins).
Therefore, if a Muslim or a person from the People of the Book (i.e. a Christian or a Jew) slaughters the animal acording to the abovementioned manner, then the slaughtering is considered Islamic (i.e. coincides with Islamic rites) and it becomes lawful to eat the meat of the slaughtered animal. However, if the animal is not slaughtered according to the above method, or that the person who slaughtered it was neither a Muslim nor from the People of the Book, then the animal's meat takes the ruling of the meat of a dead animal and it is not lawful to eat it.
Allaah Knows best.