Col. Imam was held hostage along with another former officer of ISI Khalid Khawaja and a journalist Asad Qureshi in March 2010.
The abductors had killed Khalid Khawaja but freed Asad Qureshi after his family paid ransom, sources said.
Now, Col. Imam has been killed in North Waziristan. There was no official and family confirmation of the report.