Why is benzpyrene present in tobacco smoke?

Answer 1

It is the result of a complicated chain of chemical reactions..;

Answer 2

When you "cook" a mixture of complex organic compounds, such as are found in tobacco, or indeed in any living material, you will get a wide range of additional compounds produced, as well as the original components. You would probably find it in the smoke from any fire burning plant material. That's why smoke inhalation is such a killer.