SPOKANE VALLEY, Wash. -

Spokane County Sheriff's detectives are investigating the death of a three-week old baby to determine if the death was the result of an accident or criminal mistreatment.

The baby died sometime Monday morning in the Timberline Mobile Home Park on East Wellesley in Otis Orchards. When firefighters arrived they found the mother holding her newborn son on the front porch. When paramedics asked if anyone had started CPR, the mom said, "No he's gone. He bumped his head."

That lack of CPR wasn't the only thing that first responders at the mobile home park found concerning.

“Once they got there and started rendering medical aid, they felt we needed to take a look at it due to some of the living conditions and so on,” Spokane County Sheriff Deputy Mark Gregory said.

Deputies say the mobile home was so filthy they placed the baby's 11-year-old brother with Child Protective Services and investigators later obtained a search warrant so they could seize evidence related to the infant's death.

The mother told arriving sheriff's deputies that she found her son face down, underneath the recliner in the living room, so Major Crimes detectives swabbed the footrest for the baby's DNA, trying to determine if somehow it accidentally came down on top of him.

The mom says she doesn't know where her baby was sleeping the night the night he died. According to the search warrant detectives seized the entire recliner as evidence.

“Our detectives spent most of the day out there, going though the information and looking at the evidence that's there to see if there was anything criminal or not,” Gregory said.

Spokane's medical examiner is now trying to determine the cause and manner of the child's death, which will help detectives determine if the infant's death was the result of an accident or something else.