"He said he feared he would suffer the same fate should he be re-detained," the statement continued.
"Our priority was the safety of local residents as well as the safety of the officers and the welfare of the man who had been detained," the police statement said.
Officials at Whiteman Air Force Base, whose security police detained the eight people, issued a statement saying damage at the missile sites included cut fences, slogans painted on cement and damage to an electrical outlet.
When authorities arrived, they briefly detained the woman but released her after she gave a statement.
Police detained the girl.
The coalition troops detained one militant, the statement said.
"We renew our call for the Chinese government to end harassment of those who participated in the protests and fully account for those killed, detained or missing," the statement added.
Mr Bortnikov gave no details of how and where the suspects were detained, in the brief statement carried by Russia's state-owned Channel One, but he did say the investigation was continuing.
As the facility's official mission statement declares, the institution was designed to detain the state's "most serious" convicts.
"The U.S. government will never cease its efforts to bring back our citizens who are unlawfully detained or missing overseas," the statement said.
