Brittany Gosney was charged with murder, involuntary manslaughter, gross abuse of a corpse, tampering with evidence and child endangering charges
James Robert Hutchinson
James Robert Hutchinson
| Credit: Middletown Division of Police

The Ohio mother accused of killing her 6-year-old son and throwing his body into the icy Ohio River last month is seeking an insanity defense, according to TV station WKRC.

The attorney for Brittany Gosney filed a motion in Butler County, which questioned her client's competency and stated her defense as not guilty by reason of insanity.

"Defendant struggles to assist in her defense and counsel has serious concerns regarding defendant's mental health," her attorney stated, according to the news station.

On Feb. 28, Gosney, 29, of Middletown, told police she was pressured  to "get rid of" her kids by her boyfriend, James Hamilton, 42, according to a shocking Preble County Sheriff's Office incident report obtained by the Journal-News, WKRC and The Daily Beast.

The PCSO did not respond to PEOPLE's request for comment and for the report at the time.

Brittany Gosney
Brittany Gosney
| Credit: Middletown Division of Police

The alleged crime came to light when Gosney reported her son James Robert Hutchinson missing, the Middletown Division of Police said in a statement.

Authorities stopped searching for the boy after Gosney and Hamilton told investigators during questioning that the boy was killed in Preble County a few days before he was reported missing, Middletown Police said in a statement.

A recently released incident report from the PCSO says Gosney told police she was under pressure to "get rid of" her kids – Hutchinson and his two siblings, ages 9 and 7, the Journal-News reports.

One of her other children was in foster care, WKRC reports.

Doing what her boyfriend had allegedly told her to do, Gosney drove the three children to Rush Run Park in the middle of the night on Feb. 27 with the alleged purpose to abandon them there, Middletown Police said in its statement.

"Brittany admitted she planned to get the kids out of the vehicle and leave them behind as Hamilton had been pressuring her to get rid of the kids," Preble County Capt. Andrew Blevins said in the incident report, the Journal-News reports.

As Gosney started to drive away, the terrified little boy allegedly grabbed on to the door handle of the 2005 Dodge Caravan.

James Hamilton
James Hamilton
| Credit: Middletown Division of Police

In court documents obtained by WLWT, authorities say that when Gosney drove off, she was "dragging him for a distance at a high rate of speed."

When she returned 30 to 40 minutes later, she found him in the middle of the road with a head injury, the court documents say.

"Brittany then loaded the 2 live children and Hutchinson back into the vehicle and returned to her and Hamilton's residence." the PCSO incident report says, The Daily Beast reports.

At about 3 a.m. on Feb. 28, they drove from Middletown to Lawrenceburg, Indiana, and threw the boy's body into the Ohio River, say police, the Journal-News reports.

Gosney was charged with murder, involuntary manslaughter, gross abuse of a corpse, tampering with evidence and child endangering charges. She is being held on a $2 million bond. Her next court appearance is scheduled for Monday.

Hamilton is charged with gross abuse of a corpse, kidnapping, tampering with evidence and child endangering charges. He's being held on $750,000 bond.

The pair pleaded not guilty to their charges.

Gosney's two other children have been removed from the residence.

Want to keep up with the latest crime coverage? Sign up for PEOPLE's free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Meanwhile, Middletown police have continued searching the Ohio River for the boy's body, but have remained unsuccessful, WKRC reports.

At the time of the boy's death, the child's father told WKRC he was devastated by the loss of the boy he adored. "He was really funny," Lewis Hutchinson told the station. "He just brought joy to everybody … he was a great kid. He was my world."

He also said the boy didn't have to die.

"All she had to do was give him to me," Hutchinson told WKRC. "She could have dropped him off at my sister's house. I don't understand what would drive somebody to be a monster like that."