An incestuous father who had a baby with his biological daughter killed the infant in North Carolina before murdering the girl and her adoptive father 600 miles away and then turning the gun on himself.

Law enforcement officials in three states are working to untangle the chain of events that led to the deaths of four people, among them a seven-month-old boy.

Steven Pladl, 43, was discovered dead from a self-inflicted gunshot wound inside a car parked in Dover, New York, at 8.40am on Thursday.

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Steven Pladl with his daughter Katie as a baby. The 43-year-old shot himself in Dover, New York

Steven Pladl (left) who was charged with incest involving his daughter, whom he married, killed himself in New York on Thursday. Katie Pladl (right), 20, was also found dead along with her adoptive father in Connecticut

Tiny victim: The Pladls' infant son was discovered dead by police in North Carolina Thursday

Steven and Katie got 'married' in a lakeside ceremony in July not long before she gave birth to their baby. They are pictured with her adoptive parents (right) and his mother who attended it despite its incestuous nature

Bennett was found after Steven's mother called 911 for a welfare check on the infant. She said her son told her he'd killed the baby left him there, and warned her not to go to the home

Police said other than the child's lifeless body the home was empty. It is the same home Steven and Katie shared before they were arrested for their illegal marriage

Police found the child at just before 9am at Steven's home on Earlston Ct in Knightdale, North Carolina

Pladl killed his son after picking him up from his mother's house in Cary on Wednesday night, where the child was living in her custody according to WTVR

He then drove to New Milford, Connecticut, 600 miles away, and shot dead Katie and her adoptive dad as they sat in a pickup truck, before making his way across the state line and turning the gun on himself. Pictured is the truck Steven was in when he killed himself

His biological daughter, whom he illegally married last July, 20-year-old Katie Pladl, was found dead in Connecticut along with her adoptive father, 56-year-old Anthony Fusco.

The baby boy named Bennett that Steven and Katie had together in September 2017 was discovered dead at a home in Knightdale, North Carolina, where the couple used to live, reported CBS17.

Steven Pladl was said to be still living in the home on Earlston Court.

Police who were called to the residence by Steven's mother asking to perform a welfare check at 9am came upon the boy's lifeless body.

No one else was in the home.

Pladl is believed to have killed his son after picking him up from his mother's house in Cary on Wednesday night, where the child was living in her custody according to WTVR.

He then drove to New Milford, Connecticut, 600 miles away, and shot dead Katie and her adoptive dad as they sat in a pickup truck, before making his way across the state line and turning the gun on himself.

It is thought that Steven committed the murders because Katie had just broken up with him.

'His wife broke up with him yesterday over the phone,' Steven's mother can be heard saying in a 911 recording.

During a press conference, Knightdale Police Chief Lawrence Capps confirmed all three murders and Steven Pladl's suicide

'She's in New York and he told me he was on his way to her and then he was coming back.

'He left the baby dead. He told me to call police and that I shouldn't go over there.

'He said the house is empty and he said he left a key under the front mat.'

She said Steven also told her he had killed Katie and her father.

During a press conference, Knightdale Police Chief Lawrence Capps confirmed all three murders and Steven Pladl's suicide.

'We are heart broken, saddened over the death of this child,' Capps said.

'And like you we're trying to make sense of all the factors that lead up to this senseless taking of life.'

A map shows where and when each of the bodies was found on Thursday morning

The pair tied the knot on July 20, months after Alyssa, Steven's ex-wife and Katie's biological mother, reported their relationship to police

Steven is pictured with the baby boy. He and his ex-wife gave Alyssa up for adoption when he was 22 and her mother was 20

Katie's adopted father, who was found dead alongside her in Milford, Connecticut, is pictured with his two adopted daughters and his wife

Katie (far right), her adopted father and her sister are all pictured in an old photo from her sister's Facebook page

Steven and Katie got together in 2017, after she decided to get in touch with her birth parents in June of 2016.

Not long afterwards, Steven and Katie's biological mother, Alyssa, separated and Katie and Steven started their affair.

In July 2017, the pair 'got married' and shared photographs of their lakeside union on social media.

Disgusted: Alyssa Pladl is shown holding up a picture of her daughter Katie when she was a baby

Katie gave birth not long afterwards to a baby boy. Since then, they had both doted over the newborn on Instagram.

They were arrested in January 2018 when Alyssa discovered their incestuous marriage and reported it to police.

Both were extradited to Henrico County, Virginia, to face charges of incest, adultery, and contributing to delinquency of a minor.

Steven was released on bond and ordered to remain in Virginia pending his trial and make no contact with Katie. The conditions of his bond were later amended to allow him to travel to North Carolina.

Katie was released from jail in late February after posting $12,000 secured bond. Under the conditions of her release, she was barred from making contact with Steven and required to live with her adoptive parents, who resided in New York.

In February, Alyssa told DailyMailTV how she discovered their relationship in her 11-year-old's journal.

After she and Steven separated, the 11-year-old switched between staying at her home and the home her ex-husband was in with Katie.

In the entries, the 11-year-old depicted Katie as being pregnant and described Steven as 'Satan'.

They wrote that because Katie was 'human' and Steven was 'Satan', their baby would be 'half-demon.'

Katie is shown above with her birth mother Alyssa who gave her up for adoption with Steven in 1998. They went on to have two more daughters (shown above) and it was one of those girls who exposed the older sister's affair

When Katie got back in touch with her birth family, Alyssa says her suspicions were raised when Steven insisted on sleeping of the floor of her bedroom. When he and Alyssa split up, Katie chose to live with him full time

Genetic Sexual Attraction Genetic sexual attraction is defined as an overwhelming sexual attraction that may develop between close blood relatives who first meet as adults. In the state of Virginia, incest if a criminal act. According to Virginia’s legislative information system, ‘any person who commits adultery or fornication with any person whom he or she is forbidden by law to marry shall be guilty of a Class 1 misdemeanor’ The law further states that ‘any person who commits adultery or fornication with his daughter or granddaughter, or with her son or grandson, or her father or his mother, shall be guilty of a Class 5 felony’ In Virginia, a Class 5 felony carries a prison sentence of ‘not less than one year nor more than five years’ or in the discretion of the jury or court ‘confinement in jail for not more than 12 months and a fine of not more than $2,500, either or both’ Genetic sexual attraction is said to be rare, but there have been dozens of reported cases of close relatives falling in love with each other after reconnecting as adults. In 2016, Patricia Spann, 43. and her daughter Misty Spann were arrested and charged with incest after they got married Advertisement

In March 2017, Steven presented Alyssa with the journal and said the 11-year-old was 'acting out'.

Alyssa, who was horrified, said she thought it was his way of informing her of the incestious affair.

She contacted police immediately but the pair carried on living together and in July, got married in front of Katie's adoptive parents and Steven's mother.

The baby was born not long afterwards.