MANILA -- It's "unacceptable" how the deaths of 16 prison officials in the national penitentiary since 2011 remain unsolved, Sen. Richard Gordon said Wednesday, as he led an investigation into the latest fatality.

Most of the 16 were gunned down by unidentified assailants on motorcycles, said Gordon, chairman of the Senate Blue Ribbon Committee.

"Lahat ng mga kasong yan, walang naso-solve... Nakakahiya ito na 16 napapatay, walang nasosolve. Open season," he told police and investigators who attended the hearing.

(None of those cases have been solved... It's shameful how 16 were killed and none have been solved. Open season," he said.

Sen. Richard Gordon presents a list of Bureau of Correction officials who were killed by unidentified gunmen. Gordon says none of the cases have been solved since 2011. pic.twitter.com/GStAjW92qB

— Kat Domingo (@_katrinadomingo) March 4, 2020

Sen. Panfilo Lacson, a former national police chief, said Wednesday's investigation aimed to look into the capacity of convicts to commit crimes in detention.

He also ordered law enforcers present to detail the number of cases of convicts who committed crimes outside jail when they were supposed to be incarcerated.

Sen. Ronald Dela Rosa, a former national police and prisons bureau chief, said drug lords directing killings from the National Bilibid Prisons was an open secret.

Dela Rosa said prison officials need to exert their authority over prisoners.

"Wag kayo papatakot diyan sa kanila. Kung magpapatakot kayo, tatakutin tayo... Sila ang takutin niyo,"

(Don't be scared of them. They should be scared of you instead.)