New details about the assassination of Hezbollah military chief Fuad Shukr were released on Sunday in the Wall Street Journal, It says he was killed after receiving a phone call ordering him to climb five stories to help Israel eliminate him in an airstrike.

Shukr, who was known only to a few because of his secrecy, spent his last day, July 30, in his office on the second floor of a residential building in the Dahieh neighborhood of southern Beirut, an official Hezbollah source told the newspaper.

The leader of the terrorist organization, Hassan Nasrallah, said in his eulogy for Shukr that he had been in contact with Shukr just hours before his murder.

That evening, he received a call from a man who asked him to come to his apartment, which was five floors up, on the seventh floor, where it would be easier to carry out a targeted attack given the surrounding buildings. The call apparently came from someone who had penetrated the terrorist organization’s internal communications network, the source said.

Hezbollah and Iran are continuing to investigate the intelligence glitch but are convinced that Israel penetrated the closed systems and outsmarted Hezbollah’s counter-surveillance using better technology, the source added.