Context: On 3 May, 2000, Abu Sayyaf guerillas occupied the Malaysian dive resort island Sipadan and took 21 hostages, including 10 tourists and 11 resort workers - 19 foreign nationals in total. The hostages were taken to an Abu Sayyaf base in Jolo. Two Muslim Malaysians were released soon after. Abu Sayyaf made various demands for the release of several prisoners, including 1993 World Trade Center bomber Ramzi Yousef and $2.4 million. In July, a Filipino television evangelist and 12 of members of the Jesus Miracle Crusade Church offered their help and went as mediators for the relief of other hostages. They, three French television crew members and a German journalist, all visiting Abu Sayyaf on Jolo, were also taken hostage. Most hostages were released in August and September 2000, partly due to mediation by Libyan leader Muammar Gaddafi and an offer of $25 million in "development aid". Abu Sayyaf conducted a second raid on the island of Pandanan near Sipadan on 10 September and seized three more Malaysians. The Philippine army launched a major offensive on 16 September 2000, rescuing all remaining hostages, except Filipino dive instructor Roland Ullah. He was freed in 2003. Abu Sayyaf coordinated with the Chinese 14K Triad gang in carrying out the kidnappings. The 14K Triad has militarily supported Abu Sayyaf.

Question: How many hostages were not freed by September 16, 2000?

Answer:
1