MADRID -- An 80-year-old Spanish nun has refused to testify at a court hearing about her alleged involvement in the stealing of newborn babies from their parents and selling them to other families.

Spanish police have investigated hundreds of cases amid allegations of baby trafficking dating from the years after Spain's 1936-39 civil war and supposedly a few even in the mid-1990s.

Authorities were alerted by an association of people searching for lost relatives. The group alleges the scheme involved a nationwide network, including doctors, nurses, midwives, nuns and intermediaries. Mothers were told their babies had been stillborn.

Sister Maria Gomez is the only person subpoenaed so far. She appeared in court Thursday and told the judge she would exercise her right to remain silent.

Reuters reports that Sister Maria Gomez is charged with "illegal detention and falsifying documents."

According to Newser, one mother of a stolen infant alleges that Sister Maria Gomez also threatened to steal her other child.

"Stop asking me [where the baby is] or else I will also take away your other daughter and you will go to jail for adultery," the mother claims Sister Maria Gomez said.

The BBC explains that thousands of babies are thought to have been stolen under Francisco Franco's dictatorship with the aim of removing children from their "undesirable" left-wing parents and placing them under the care of "approved" right-wing families.