GAITHERSBURG, MD — A Gaithersburg mother has pleaded guilty to murder for poisoning her son with an allergy medicine before a fiery car crash that she caused in an attempt to hide her crime, authorities say.

Montgomery County Police charged Narges Shafeirad, 34, in August 2015 with first-degree murder and first-degree arson in the death of her 5-year-old son, Daniel Dana. Shafeirad's vehicle was reported on fire June 16, 2015, off the road near the westbound lanes of Sam Eig Highway (Route 370) and Fields Road.

On Thursday she pleaded guilty to the murder, arson and child abuse in Montgomery County Circuit Court, according to Maryland online court records. A sentencing date has not yet been set for Shafeirad.

SEE ALSO: Child Dies in Car Crash, Fire: Police

Mother Charged with Son's Poisoning, Murder: Police At the crash scene, Montgomery County Fire and Rescue personnel saw Shafeirad with the vehicle; she told first responders her son was inside the car. Rescuers attempted to force open the vehicle, breaking glass, and then extinguishing the fire, but were unable to remove the boy.

Shafeirad was treated at an area hospital for second- and third-degree burns over 40 percent of her body.

Capt. Darren Francke, commander of the Montgomery County police department's major crimes unit, said the child was killed by an overdose of Diphenhydramine, an antihistamine used in allergy medicine, including Benadryl. Shafeirad reportedly told police she forced the boy to drink an entire bottle of the medicine.

The boy's mother gave him "an extraordinary amount, an excessive amount" of the medicine, then set the fire to obscure the crime, Francke said at the time of her arrest. Daniel was dead when he was placed in the car, Francke said, and didn't suffer from the fire.