VeraCrypt is open-source and free software. The complete source code of VeraCrypt (written in C, C++, and assembly) is freely available for peer review at:
https://sourceforge.net/p/veracrypt/code/ci/master/tree/
https://github.com/veracrypt/VeraCrypt
https://bitbucket.org/veracrypt/veracrypt/src
The source code of each release can be downloaded from the same location as the release binaries.