The mystery over the killing of an Andhra student in the US state of Missouri deepened on Tuesday with the discovery of the body of an Indian man in a lake near the spot she was found shot dead.

The body of Soumya Tummala, a 22-year-old electrical engineering student at Southern Illinois University in Edwardsville, was spotted by passersby inside a car near the Sunfish Lake boat ramp in Spanish Lake area at about 8.30 am on Sunday.

Detectives searching the area for clues found the body of Vikram Kumar Tummala, 27, in the lake three hours later, local newspapers St Louis Post and Belleville News Democrat reported.

He has also died of a bullet wound, they said.

Police said they believe Vikram Tummala is related to Soumya Tummala, but is not her husband or brother. They lived at different addresses in Maryville.

St Louis County police did not discuss specific details and stopped short of calling the shootings a murder-suicide, but they said no one else was involved, according to the Post.

The Ford Taurus car, in the passenger seat of which Soumya's body was found, was registered in Vikram's name, the police said.

"What we're trying to find out now is why these two individuals from Maryville, Illinois, were up in such a remote area of St Louis County," police spokesman Rick Eckhard said.

He said a relative of Soumya flew to the area and identified her body. "The investigation will continue as we work with the medical examiner's office and interview family and friends," Eckhard said.