Detroit ? In a case that shocked authorities in a small western Michigan city, a man stands accused of striking a deal for sex not only with the 14-year-old daughter of his girlfriend – who police say offered the girl to him while she recovered from surgery – but with his own 12-year-old daughter.

“I’ve never seen anything like this before. Parents aren’t supposed to do something like this,” Calvin Mahan, a detective with the Muskegon Heights police, said Friday.

Because the Detroit Free Press does not publish the names of the alleged victims of sex crimes, the man and woman are not being identified to protect the identities of the two children.

According to authorities, the 37-year-old man’s girlfriend persuaded her daughter to sign a contract obligating the then-14-year-old girl to have sex with him in exchange for clothing and body piercings. Police said the woman was worried the man would dump her while she was recovering from tummy tuck surgery.

Authorities said the mother, daughter and the man all signed the contract. The man and the girl allegedly had sex about 20 times from June 6 to July 15, during which time she turned 15 years old.

“Basically, mom was pimping out her daughter,” Mahan said.

On Friday, Mahan said authorities also learned that the man had given his own daughter – who had been staying with him after living with her biological mother – packs of cigarettes for sex. According to the Muskegon County Prosecutor’s Office, the man had sex with his daughter from sometime in November to July 15.

In the case involving his daughter, the man is charged with six counts of first-degree criminal sexual conduct with a child under age 13; in the other case, he is charged with six counts of third-degree criminal sexual conduct with a child 13 to 15 years old.

If convicted on the charges involving his daughter, the man could be sentenced to life in prison; for those involving his girlfriend’s daughter, he could serve up to 15 years in prison.

Meanwhile, the girl’s mother has been charged with three counts of aiding and abetting third-degree criminal sexual conduct with a child 13 to 15 years old. She was freed on a $25,000 bond after being arraigned Tuesday. She could face 15 years in prison if convicted.

Her children, including a son and another daughter, were removed from her home.