Girl gives teacher note about her mom's boyfriend. Then the body of her 4-year-old brother was found in a freezer a day later.

The body of a young boy was found in a freezer at a Las Vegas home after his sister handed her teacher an alarming note about her mother's boyfriend – which triggered a police investigation.

A young girl gave her elementary teacher a note that was written by her mother. The note said that the mom was being held captive in her home and she was concerned about her missing son, according to Las Vegas homicide Lt. Ray Spencer.

"She stated that she didn't know where her younger child was and that she believed he was deceased," Spencer said of the mother's note.

The teacher alerted authorities shortly after 8:30 a.m. on Tuesday, which prompted Las Vegas Metropolitan Police Department officers to begin surveilling the family's home in northeast Las Vegas, according to the arrest report.

Around 10 a.m. on Tuesday, Brandon Toseland and his girlfriend left the home in a white Nissan sedan. Police noticed a handcuff attached to the front seat, where Toseland's girlfriend was seated, according to the arrest report.

Police officers questioned the woman, who reportedly confessed that Toseland confiscated her cellphone. She also revealed that her boyfriend of 11 months was "bounding/tying her" up and would "handcuff her inside the vehicle, preventing her freedom of movement," the report stated.

"This claim was further substantiated with the handcuff being observed in plain view in the vehicle," police investigators allegedly wrote, according to the Reno Gazette-Journal.

"She said she was not allowed to leave the house alone or go into the garage," the mother said, according to Spencer.

The mother allegedly told authorities that she had last seen her son on Dec. 11. She purportedly informed investigators that Toseland locked her 4-year-old son, Mason Dominguez, in the master bedroom of the home after the boy became ill in early December.

The Gazette-Journal reported, "Toseland eventually admitted to his girlfriend that her son was dead, according to the report, claiming it was an accident."

Toseland — who is not the father of the children — was arrested and charged with two counts of first-degree kidnapping.

Police obtained a search warrant on Tuesday afternoon. Investigators discovered the 4-year-old's body in a freezer "hidden under a false cardboard bottom and under multiple items of food," according to police.

On Wednesday, Tosleand was rebooked into a Las Vegas jail on a murder charge.

"But it’s still early on, and there are a lot of questions that we still have to answer about what occurred over the last three months," Spencer said.

The New York Post reported, "Police Lt. Ray Spencer said 'there are a lot of questions that we still have to answer about what occurred over the last three months,' but that investigators don’t believe the mother was involved in her son's death."

Since 2005, Toseland has been arrested for domestic battery and disorderly conduct, court records show.

Stephen Stubbs — a lawyer representing the woman — told Fox News, "There was never a time when her daughter was with her that she was not locked in a room, bound or handcuffed. There was never an opportunity to take her daughter and run."

"The mother was physically, sexually, and emotionally abused," Stubbs added. "The children were physically and emotionally abused and separated from their mother most of the time."

The woman's 7-year-old daughter was reportedly placed in the care of relatives.

Relatives described Mason Dominguez as "happy, sweet, intelligent, very outgoing" in a fundraising campaign for the boy's funeral costs. The family hopes to bury Mason next to his father — Elijah Dominguez — who died unexpectedly in January at the age of 29.

Family identifies Las Vegas boy, 4, found in freezer; man accused of killing him appears in courtwww.youtube.com