Police investigating the slayings of seven women whose bodies were found over the weekend said Monday they believe it is the work of a serial killer, and that the suspect has indicated there could be more victims going back 20 years.

Prosecutors in Lake County in the Midwestern state of Indiana on Monday charged 43-year-old Darren Vann in the strangulation death of 19-year-old Afrikka Hardy. Her body was found Friday night at a Motel 6 in nearby Hammond.

Gary officials were expected to charge Vann later this week in the deaths of six more women, whose bodies were found Saturday and Sunday. Hammond Police Chief John Doughty said at a news conference that Vann confessed to Hardy's slaying and gave police information that led to the other bodies in Gary, including three on the same block.

Darren Vann is a suspect in the slayings of seven women whose bodies were found in northwestern Indiana over the weekend. (Lake County Sheriff's Department/Associated Press)

Vann was a convicted sex offender in Texas, where he pleaded guilty to raping a woman in 2009 and was released from prison in July 2013.

The Austin Police Department issued a statement Monday saying it would review missing persons and cold cases to determine if there could be a link to Vann, and asked anyone with information to come forward.

Doughty said police have no specific indication that any slayings have occurred in another state, and the slayings in Gary appeared to have happened recently. He said Vann is co-operating with investigators in the hope of making a deal with prosecutors.

"It could go back as far as 20 years based on some statements we have, but that has yet to be corroborated," Doughty said.

The Texas Department of Public Safety listed his risk level as "low" on its sex offender registry. He did not register in Indiana.

Court records in Travis County, Texas, show that Vann served a five-year prison sentence, with credit for the 15 months he was in jail awaiting trial, after pleading guilty in 2009 to sexually assaulting a woman at an Austin apartment two years earlier.

The woman told police that she went to Vann's apartment, where he asked if she was a police officer. After she told him no, he knocked her down and began to strangle and beat her, hitting her several times in the face and telling the woman he could kill her. He then raped her.

Vann allowed the woman to leave and she called police the next day.

'Suspicious' texts triggered police call

Indiana authorities said Hardy, the woman Vann is accused of strangling, was involved in prostitution and had arranged to meet him at the Motel 6 through a Chicago-area website. Police were called by someone who attempted to reach Hardy and "was provided suspicious text responses that she believed to be from the suspect while he was still inside the motel room."

Police said they took Vann into custody Saturday afternoon after obtaining a search warrant for a home and vehicle in Gary.

They found the body of 35-year-old Anith Jones of Merrillville, Ind., on Saturday night in an abandoned home. She had been missing since Oct. 8.

The bodies were found in the area of Gary, Ind. (Google Maps) Five more bodies were found on Sunday in other homes, said Doughty, who identified two of the women as Gary residents Teaira Batey, 28, and Christine Williams, 36. Police have not determined the identities of the other three women, including two whose bodies were found on the same block where Jones' body was found on Saturday.

Gary Mayor Karen Freeman-Wilson said only Jones was reported missing, perhaps indicating that Vann "preyed on individuals that might be less likely to be reported missing."

Hardy's mother, Lori Townsend, said police told her that Vann asked that Hardy perform a certain sex act, and "when she said 'no' and put up a fight, he snapped and strangled her."

"This man is sick," Townsend said from her home in Colorado.

Hardy graduated from high school in late 2013 and planned to go to college to study music, Townsend said.

"She was full of life. She lit up a room with her smile and her beauty," she said. "And she had a voice like a songbird."

Gary, once a thriving steel town of 178,000 where thousands worked in the mills, has been struggling for decades. Its population has shrunk to just over 78,000 and its poverty rate hovers around 40 per cent. Thousands of homes are abandoned, many with weeds choking broken sidewalks — often on the same streets where other homes are tidy and well-kept.