71. Is it specified that a particular institution(s) is responsible for investigating money laundering that relates to political parties, candidates and elected officials?

Not mentioned explicitly in the Federal investigation Agency Act, 1974 or in the Anti-Money Laundering Act, 2010 but de facto is the agency whose powers allow it to investigate money laundering cases related to political parties. See e.g. below:

'The Federal Investigation Agency has registered a money-laundering case against Muttahida Qaumi Movement founder Altaf Hussain and his party leaders. The case registered also pinpointed illegal transfer and misuse of funds received by the party’s charity wing, Khidmat-e-Khalq Foundation (KKF)'

Source: The Nation (2017) 'FIA books Altaf, others for money laundering', available at: https://nation.com.pk/03-Oct-2017/fia-books-altaf-others-for-money-laundering, accessed: 14/03/2018.

The Federal Investigation Agency is tasked with investigating money-laundering cases.