Who prosecutes election-related criminal offences?

Poland
Answer
Public prosecutor
Source
Constitution of Poland
http://www.worldlii.org/pl/legis/const/1997/1.html#C8S1
Article 101: (1) The Supreme Court shall adjudicate upon the validity of the elections to the House of Representatives (Sejm) and the Senate.
(2) A voter shall have the right to submit a complaint to the Supreme Court against the validity of the elections in accordance with principles specified by statute.
Article 129: (1) The Supreme Court shall adjudicate upon the validity of the election of the President of the Republic.
(2) A voter shall have the right to submit a complaint to the Supreme Court concerning the validity of the election of the President of the Republic in accordance with principles specified by statute.
Election Code (Act of 5 January, 2011)
http://www.legislationline.org/download/action/download/id/3648/file/Poland%20Elections%20Code%20Section%201,2,3,4,9_2011.pdf
Article 243: ? 3 If the complaint concerns the committing of a crime against the elections, the Supreme Court shall immediately notify the Prosecutor General.