Authorities responded to a call to the 3300 block of Billie Court just after 7 a.m. and discovered the bodies of a woman and a man.
"When (neighbors) looked outside the front of their residence, (they) believed what they saw was just an injured person," said Stephanie Shannon of the Simi Valley Police Department. "When the fire department arrived on scene, they actually were able to locate two deceased people here in front of the residence."
Officials believe that the man shot and killed his neighbor, and then killed himself.
"It's kind of scary," said neighbor Mary Bernberg. "You didn't expect that to happen in your neighborhood."
Police say they have not determined a motive for the apparent murder-suicide, but according to several neighbors, there had been a long-running feud between the two deceased people.
"Like every neighborhood, you can have a little tit for tat, but to bring it to that level is ridiculous," said Dan Johnson of Simi Valley.
Friends of the victims came by to see for themselves what happened. One man who says he worked with the woman came by because she didn't show up to work Tuesday morning. He was stunned to hear the news.
"She had a good heart, a nice person to work for," said the man, identified only as Dave. "That's scary to hear that happened to her. A nice lady."
Police said a gun was found at the scene.
The investigation is ongoing. Anyone with information related to the case is urged to call Ventura County Crime Stoppers at (800) 222-TIPS.