LONDON — Police detectives investigating the case of three women who claim to have been held against their will for 30 years said Friday that the victims had been brainwashed and imprisoned by “invisible handcuffs” in an unremarkable house in South London.

A police commander leading the investigation also revealed that a couple in their 60s, arrested Thursday on suspicion of holding the three women, had also been detained in the 1970s, but he refused to elaborate. The two suspects, both 67 and unidentified under police protocol, were released on bail late on Thursday after surrendering their passports.

“What we have uncovered so far is a complicated and disturbing picture of emotional control over many years,” Commander Steve Rodhouse of the Metropolitan Police said at a news conference. “Brainwashing would be a simple term, but I think that belittles the years of emotional abuse these victims have had to endure.”

Commander Rodhouse said the case was different from others involving domestic servitude because it was “not as brutally obvious as women being physically restrained inside an address and not being allowed to leave.”