The four investigators had arrived in Islamabad on Dec 13 and interviewed several people. One of them, Ms Viraic Right, left Islamabad earlier and the other three, Ms Marcie Mersily, Mr Suman Pradhal and Mr Milbert Shin, on Monday.
The seven other members of the team were from the security wing.
The team began its probe in January this year and visited Liaquat Bagh where Ms Bhutto was killed in a gun-and-bomb attack.
Official sources said that the reason for the team cutting short its visit appeared to be a change in the schedule of arrival of three members of the fact-finding commission, Chilean Ambassador to UN Heraldo Munoz, former Attorney General of Indonesia Marzuki Darusman and Peter Fitzgerald, a veteran of Irish national police.
They were first scheduled to arrive in Islamabad on Dec 18, and then on Dec 22, but their visit was postponed again.
