Image copyright CBS Image caption Steven Pladl, 42, and his biological daughter Katie Rose Pladl, 20

A US man in an incest case has reportedly killed his biological daughter, their child, and the girl's adopted father, before killing himself.

The murder-suicide by Steven Pladl spanned three states, authorities told local media.

North Carolina police began a search for Pladl, 42, after his mother called police, saying her son had confessed to the killings.

Katie Pladl and her adoptive father, Anthony Fusco, were later found dead.

Police in New Milford, Connecticut, found the bodies of Ms Pladl, 20, and Mr Fusco, 56, in a truck that had its windows shot out on Thursday morning.

The suspect was later found in upstate Dover, New York, in a minivan, dead from an apparently self-inflicted gunshot wound, WTVR-TV reports.

Image copyright CBS Image caption Katie and her adoptive father were found shot to death inside a truck in Connecticut

Last January the father and daughter were arrested in Virginia and charged with incest.

Katie Pladl reconnected with her biological parents at the age of 18 through social media.

She became pregnant shortly after moving in with them.

Pladl's wife - Katie's biological mother - moved out, telling police he planned to wed their daughter.

In March, Pladl was released from jail on bail, on condition he not make contact with his biological daughter.

According to a 911 call obtained by WTIC-News, his mother called to report he had admitted the killings to her.

"My son just called me. He told me... he killed his baby and he's in the house," she tearfully told emergency officials.

"He killed his wife. He killed her father. I can't even believe this is happening."

She added that "his wife broke up with him yesterday over the phone".

Pladl's mother had been granted custody of her son's seven-month-old son, Bennett, as part of his bail agreement.

The day before the murders, he picked up his son from her, saying he planned to take the child to New York to see his mother.

Police in Knightdale, North Carolina, discovered the infant's body on Thursday.

Knightdale Police Chief Lawrence Capps said: "We are heartbroken, and saddened over the death of this child and like you, we are trying to make sense of all the factors that led up to this senseless taking of life."

Chief Capps added that Pladl had driven to New York "for the specific purpose of making some confrontations".

Pladl's lawyer Rick Friedman told WNCN-TV in North Carolina that Mr Fusco and Ms Pladl were shot, and "then Steven took his own life".

"This is a terrible tragedy that nobody foresaw," Mr Friedman said.

"I really believe that if the judges or the prosecutor or the defence attorneys in this case had any clue that the minor child or anyone would be harmed there would not be a bond set for any of the parties," added Mr Friedman.