Hackett was addressing a press conference at the Police Adminstration Building, Edward Street, Port-of-Spain.
The 11 charged are, Rajaee Ali, his brother Hamid Ali, Devaughn Cummings, Ricardo Stewart, Earl Richards, Stephan Cummings, Ishmael Ali, Kevin Parkinson, Leston Gonzales, Roget Boucher and Gareth Wiseman
The men are also charged with offences under the Anti-Gang Act. Rajaee Ali is charged with being a gang leader. His wife, Stacy Ali is also charged under the Anti-Gang Act along with Dion Peters and David Hector.
Yasin Abu Bakr, Hassan Ali, Keston Modeste and Keston Seales have been released without charge.
Hackett admitted this was the most challenging investigation he has worked on and confirmed that the TTPS sought assistance from international law enforcement agencies.
He said if more information comes to hand, the case could be re-opened to charge others with Seetahal's murder.
The 11 men will appear before the Chief Magistrate on Monday, July 27.
Seetahal was murdered on May 4, last year, as she was leaving a casino in Woodbrook.