Why the delay?

A United Nations investigative report into the assassination of Benazir Bhutto was due to be released March 31 (i.e., today). The NYT reports (temporary link)

U.N. Secretary-General Ban Ki-moon has accepted an urgent request from Pakistan to delay presentation of a U.N. report on the 2007 assassination of former Pakistani Prime Minister Benazir Bhutto, the world body said on Tuesday.

The report on a nine-month inquiry by a three-person U.N. panel, was originally due to be presented by Wednesday, but Pakistani President Asif Ali Zardari requested it be delayed until April 15, U.N. spokesman Martin Nesirky said.

Nesirky gave no reason for the Pakistani request.

Anujan on BRF speculates based on some news-items that this is an effort to bury the report altogether. But why?

Nesirky told reporters that the report was completed and was ready for delivery. But he said neither Secretary-General Ban nor the Pakistani government had seen it.