A year and a half after a woman was killed at a Washington state home, her ex-brother-in-law and two others have been arrested in connection to her murder.

Kevin Lewis, who was already in jail on an unrelated charge, was arrested on charges of aggravated murder with a firearm, conspiracy to commit murder and solicitation to commit murder for the September 2017 death of Alisha Canales-McGuire.

Canales-McGuire, 24, was shot in Everett, Washington, while babysitting for her sister, who was out of town, the Snohomish County Sheriff's Office said. Investigators believe the sister and not Canales-McGuire was the intended target.

Authorities allege that Lewis hired a teenage boy and girl to carry out the murder of his ex-wife.

"The male suspect posted photos on social media showing off several hundred dollar bills just a few hours after the murder. The female suspect allegedly bragged to several acquaintances that she’d been hired to kill someone in Snohomish County," the sheriff's office said.

A spokeswoman for the sheriff's office told KING-TV that investigators always believed Canales-McGuire's sister was the intended target but did not have evidence.

There wasn't a break in the case until officers received a call recently from someone who said they were at an event where a woman was talking about how she was hired to kill someone in Snohomish County, where the murder of Canales-McGuire took place.

The spokeswoman said the detectives learned that the woman bragging about the murder had once dated Lewis' cousin. Investigators then obtained search warrants and phone records.

"There was evidence out there. The detectives just needed to find it, and once they found it, it was literally like taking a thread on a sweater and the whole thing came undone," the spokeswoman said.

Lewis was already behind bars after being sentenced in 2018 to 39 months in prison for assaulting his ex-wife. He was arrested and charged for the murder of Canales-McGuire.

The male suspect, now 20, was arrested and charged with aggravated murder with a firearm and conspiracy to commit murder. He is being held at the Snohomish County jail. The female suspect, now 17, was arrested on the same charges and is being held at the Denney Juvenile Justice Center.