According to a January 2018 press release from the San Diego County District Attorney’s Office, after identifying Elizabeth’s body, “San Diego Homicide Detectives continued their investigation and identified the suspect in Elizabeth’s murder to be her former husband, Matthew Sullivan.”
The release says authorities arrested Sullivan outside his home in Wyoming, Delaware on Wednesday morning, January 31, 2018.
“He’s been arrested in Delaware and will be extradited to San Diego to face a charge of murder,” Steve Walker, Communications Director for the San Diego County District Attorney’s Office, told Dateline in an email. “Once we have him in custody, an arraignment date will be set.”
A felony complaint obtained by Dateline NBC states Matthew allegedly murdered Elizabeth "[on] or about and between October 13, 2014 and October 14, 2014." The complaint alleges Matthew used a knife to do so.