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ARAPAHOE COUNTY, Colo. -- A man was arrested Friday on charges of first-degree murder and sexual assault for an incident in an apartment Wednesday morning.

Brandon Johnson, 26, is accused of sexually assaulting the mother of his 2-year-old child before killing his own 6-year-old son on East Harvard Avenue near South Quebec Street.

The dead boy's mother, Rachel Johnson, identified him as Riley Johnson. She lives in Castle Rock and said her ex-husband had full custody of Riley.

She said she had not seen her son in about a year. She said she lost custody when she was investigated for child abuse.

Arapahoe County Sheriff's Office investigators arrested Johnson while he is still being treated in the hospital for self-inflicted knife wounds.

"He is now being detained while continuing his medical treatment until he can be transported to the Arapahoe County Detention Facility. There is no estimate on when that may take place," a news release said.

Arapahoe County Sheriff's Deputy Bill Foreman Jr. was critically injured in a crash while he was on his way to the homicide scene Wednesday morning. It happened about a mile away at East Iliff Avenue and South Valentia Street at 5 a.m.

He remained hospitalized in critical condition. Foreman's family made a statement Friday night expressing gratitude for the support he has received.

“We want to thank the community for their continued support for Bill, and for us as Bill continues his recovery. While we remain at Bill’s side hopeful for continued positive changes in his condition, we are comforted by the thoughts and prayers from the community. We are so thankful for the talented team of medical professionals who are giving their all, in the ongoing effort to save Bill’s life. We are, at the same time, overwhelmed and grateful.”

Bonfils Blood Center has set up the Arapahoe County Sheriff's Office replenishment blood drive. You can donate on behalf of Foreman by mentioning site code B016 when donating at any Bonfils community donor center.