A woman who formerly worked as a housekeeper for the victims has been arrested in connection with a home-invasion robbery allegedly committed by her stepson and an accomplice last month.

The robbery took place around 4:15 am on September 12, at a home on Wood Valley Road, just outside the town of Sonoma. Two male suspects in their 20s entered the home, according to the Sonoma County Sheriff's Office, and restrained three individuals, including the elderly couple living there. The suspects then demanded valuables and threatened the victims, with one of the suspects striking one of the victims over the head with a blunt object.

As KTVU reports, sheriff's detectives tracked down the two men they believed were responsible for the home-invasion, and they were arrested at a casino in Middletown, in Lake County. Those suspects were identified as 20-year-old Hugo Matamoros-Acosta of Hidden Valley Lake (Lake County), and 22-year-old Sincere Rush Tanner of Santa Rosa.

A search warrant turned up a firearm in Tanner's vehicle that investigators say was used in the robbery.

Now, as the sheriff's office explains on Facebook, Matamoros-Acosta's stepmother, 52-year-old Norma Matamoros of Hidden Valley Lake, has been arrested as well — apparently for being the mastermind behind the crime.

Matamoros was reportedly brought in for questioning about the robbery on October 1, and she was later booked into Sonoma County Jail alongside her stepson, on charges of elder abuse, vehicle theft, robbery, assault with a deadly weapon, conspiracy, and kidnapping. She is being held on $1 million bail.

The Sonoma County Sheriff’s Office says it is still actively investigating this case, and if you have any details that could help the investigation, you are asked to contact the Sonoma County Sheriff’s Office at 707-565-2121.

Photo via Sonoma Sheriff/Facebook