The sources later confirmed that the 25-year-old assailant was also part of a more recent investigation into a network recruiting jihadists for the fight in Syria.
During failed negotiations with police that ended with elite RAID officers storming the house, the attacker claimed he was also acting on behalf of IS.
He repeatedly stabbed the policeman and then killed his partner, who was found with knife wounds to her neck.
The couple's three-year-old son was found after the police operation, "in shock but unharmed," a prosecutor added.