The Jacksonville Sheriff's Office said a mother arrived to her Southside home Friday evening to find her daughter and her daughter's male friend dead.
Police said they found a gun and believe one of the young people pulled the trigger.
"It is still very early on, but all indications seem to point to murder-suicide. We have quite a bit more evidence to recover and analyze and make a final determination," said JSO Sgt. Jay Farhat.
Farhat said the couple was in their 20s and their identities would not be released until sometime in the weekend.
Scott Cason lives down the street from where the incident took place. He said he didn't know the family, but that he is familiar with the neighborhood. For Cason, the deaths are surprising and heartbreaking.
"This is a really quiet neighborhood. This kind of thing is really sad but it's all too common now, isn't it?" said Cason.
In fact, the deaths would mark the sixth murder-suicide in Duval County this year, as well as the 10th such event in Duval's surrounding counties this year.
"We're still not positive on that if they are boyfriend, girlfriend or what, but they have known each other for quite a while," said Farhat.