Authorities say Steven Pladl, a 42-year-old accused of having a child with his 20-year-old daughter, killed their infant son and then her and her adoptive father earlier this week. Finally, he killed himself.
The apparent murder-suicide comes only months after the case was first brought to light.
In January, Pladl was arrested for allegedly impregnating his biological daughter, Katie Pladl, whom he placed for adoption when she was a baby. They reunited two years ago.
According to warrants obtained by PEOPLE, Pladl’s ex-wife — Katie’s biological mother — first notified police of the possible relationship last May. She had read an entry in one of Katie’s journals in which the girl discussed being pregnant with her biological father’s love child.
Steven and his wife placed Katie for adoption when he was 22 and she was 17. The couple stayed together until divorcing last summer, according to court records.
When Katie turned 18 in 2016, she tracked her birth father down through social media.
The ex-wife told police she believed Steven psychologically manipulated Katie.
Katie and Steven married in July and in September welcomed a baby boy in Virginia before moving to North Carolina, where they were arrested, according to CBS News. In addition to incest and adultery, Katie and Steven were both charged with contributing to delinquency.
On Thursday morning, police in Knightdale, North Carolina, responded to a call from Steven’s mother requesting a welfare check on her young grandson, Bennett, Police Chief Lawrence Capps said at a news conference on Thursday.
The night before, Steven had picked Bennett up from his mother, who had custody of the boy, Capps said.
The grandma became worried for Bennett after an alarming phone conversation with Steven, though Capps declined to go into detail, citing the ongoing investigation.
Upon arrival at the home Katie and Steven had shared before their arrests, authorities discovered their son deceased and alone, Capps said.
A cause of death has not been released.
Later Thursday, Katie was declared the victim of a double homicide in New Milford, Connecticut, Capps said. She was slain alongside her adoptive dad, 56-year-old Anthony Busco.
Authorities believe Steven killed his son before driving to Connecticut to kill Katie, Busco and then himself in Dover, New York, Capps said. According to local reports, all three had been fatally shot.
“We’re trying to make sense of all the factors that led up to this senseless taking of a life,” Capps said of the child’s death, calling it “tragic.”
In February, Steven posted his court-mandated bond in his incest case but was required to stay in Virginia and away from Katie until trial. However a month later, a judge allowed Steven to amend his bond and travel to North Carolina, according to local station WTVR.
Katie was also released in February on the condition that she live with her adoptive parents in New York, WTVR reports. However, she was allowed to travel out of state.
• With CHRIS HARRIS
This article originally appeared on PEOPLE