Imam al-Shafi'i (may Allah have mercy on him) said: The meaning of that, and Allah knows best, is that it was not made lawful to wage war against it so that it becomes like other places. When Asim bin Thabit and Khubayb were killed, the Prophet (peace and blessings be upon him) ordered that Abu Sufyan be killed by stealth in a house in Makkah if he could be overpowered, and this was at the time when it was sacred. This shows that it does not shield anyone from something that has become due upon him, and that it is protected only from having war waged against it as war is waged against other places.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18784