Investigators are looking for a man they allege killed four relatives of a Tennessee baby who was found abandoned alive this week in sweltering heat, the Tennessee Bureau of Investigation said on Thursday.

Austin Robert Drummond, 28, is wanted in connection with the deaths of James M. Wilson, 21; Adrianna Williams, 20; Cortney Rose, 38; and Braydon Williams, 15, whose bodies were found on Tuesday in Tiptonville, a town in north-west Tennessee’s Lake County, the TBI said.

The four were found dead hours after Wilson’s and Adrianna Williams’ baby daughter was found abandoned on Tuesday afternoon in a car seat in a “random” front yard near the Dyer County community of Tigrett, nearly a 40-mile (64 kilometre) drive southeast of Tiptonville, authorities had said.

The TBI hasn’t said what led it to name Drummond as a suspect, or whether investigators know of a motive in the killings or why the baby was abandoned a county away from where the bodies were found.

Rose was the baby’s maternal grandmother, and Braydon Williams was the baby’s maternal uncle, according to Danny Goodman, district attorney for Dyer and Lake counties.

“The victims were all from Dyer County, and we suspect the person that killed them knew all of them,” Goodman, who also confirmed Wilson and Adrianna Williams were the baby’s parents, told CNN.

Warrants for Drummond, who “should be considered armed and dangerous,” have been issued charging him with four counts of first-degree murder, one count of aggravated kidnapping, four counts of felon in possession of a firearm and one count of possession of a firearm during the commission of a dangerous felony, the TBI said.

A reward of up to $2500 ($AU3866) is being offered for information leading to Drummond’s arrest, the TBI said.

Baby found abandoned hours before bodies discovered

The investigation began on Tuesday afternoon when the baby was found in a car seat in a front yard near Tigrett, the Dyer County Sheriff’s Office said.

Investigators, spurred by a 911 caller who saw the child, were checking reports that a “dark-coloured minivan or a white mid-size SUV” had left the baby there, the sheriff’s office said; the heat index was 116 degrees (46 degrees Celsius). 

The baby girl is approximately 7 months old, Goodman said.

Hours after the baby’s abandonment, the sheriff’s office announced four people – later identified as the baby’s relatives – were found dead in Tiptonville.

The bodies were found on Tuesday along Tiptonville’s Carrington Road, the TBI said without elaborating.

The TBI, when CNN contacted it with questions about the investigation, referred only to its news releases. The releases do not detail how the four were killed, how they were found, whether investigators know of a motive, or who may have left the baby in the yard near Tigrett.

“This is a deeply saddening day for our community,” Dyer County Sheriff Jeff Box said in a Facebook post on Tuesday. 

“We are committed to uncovering the truth and ensuring justice is served.”

Nearly a dozen agencies are working on the case, including the FBI and a US Marshals Service fugitive task force, the TBI said.