The death of a Missouri woman and her 3-year-old daughter last week was determined as a murder-suicide. Police said Tuesday they were investigating the case to find why the mother killed her child before shooting herself.

Bridgeton police Maj. Mark Mossotti identified the victims as Kanisha Richardson and Ava Richardson. The bodies of the woman and her child were found dead in their parked vehicle in Nottingham Lane in Bridgeton on Sunday.

Police said the gun used in the incident was recovered from the vehicle, the St. Louis Post-Dispatch reported. No suicide note was found from the scene.

Initial reports said Ava was 2 years old; however, Mossotti said Tuesday that she was born in 2017. The child would have turned 4 Monday, two days after she died, NBC-affiliated KSDK reported.

To mark Ava's birthday, friends and relatives released pink balloons in her memory.

The incident came to light after a missing report was filed last Wednesday for Kanisha and Ava. Mossotti told local media the mother-daughter duo were last seen two days earlier, on Jan. 11.

As part of the investigation into the missing report, the Missouri Highway Patrol issued an endangered missing person advisory, saying that Kanisha had made suicidal statements and was possibly carrying a gun while with the child, St. Louis Post-Dispatch reported.

Police later found the bodies inside an SUV parked at the apartment complex. Authorities are investigating the incident to find a motive behind the murder-suicide incident.

Last week, in another murder-suicide incident in California, a father killed his 9-year-old son before shooting himself. Authorities said a recent argument with his wife over getting their son vaccinated led to the deaths. Local police also said the boy's parents were involved in several legal battles dating back about five years. The child was identified as Pierce O’Loughlin.

“I think it is undeniable that Pierce’s father suffered from untreated mental illness which resulted in his taking the life of his son and his own life,” family law attorney Lorie Nachlis said, according to Kron4.

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Representational image Getty Images/Jonathan Alcorn