Cota, the man police believe shot Mendez, had reportedly turned the gun on himself, in what police say was a possible murder-suicide attempt.
He was taken to the hospital in critical condition at the time.
Police say there was a history of domestic violence between Mendez and Cota.
"Information gathered by the criminal investigations bureau has revealed the two subjects knew each other," Officer Jaret Redfearn of the Avondale Police Department said.
The gun believed to have been used in the shooting was located at the scene.
Investigators on the scene are still sorting out the moments leading up to the numerous shots fired calls that came into the 911 system shortly after noon.
"Information that we have right now is that there was [sic] multiple shots fired," Redfearn said,
Best Buy released the following statement:
Our thoughts and prayers are with the family, friends and children of Melissa Mendez after she was senselessly shot and killed on Monday. Domestic violence has no place in our society, and this tragic event is an example of how destructive it can be. Melissa, an employee at our Avondale store for more than seven years, was well-liked by her colleagues and great at her job. Counseling has been made available for our employees. Our Avondale store remains closed at this time.
A Go Fund Me account has been set up to help pay for her funeral as well as expenses for Mendez's two children.
Copyright 2017 KPHO/KTVK (KPHO Broadcasting Corporation). All rights reserved.