A 17-year-old boy killed a 14-year-old girl, before taking his own life, during a house party on Saturday evening, investigators allege.

The teenagers were discovered in a home near St. Petersburg, where the suspect was dogsitting.

"Once deputies arrived on-scene, they located 14-year-old Sayuri Jade Ruiz deceased, suffering from a gunshot wound to the head. Deputies also located 17-year-old Hector Pfeiffer, with a self-inflicted gunshot wound to the head," officials from the Pinellas County Sheriff's Office said in a statement.

"Pfeiffer was transported to the hospital and pronounced deceased at 10:16 p.m."

Pfeiffer invited Ruiz and another teenage girl to come over to the home in the early hours of Saturday morning. The suspect had only known Ruiz and the other girl for about a month - he had met both on dating apps.

After being joined by an 18-year-old friend of Pfeiffer, the group "consumed alcohol, marijuana and cocaine throughout the day," the sheriff's office alleges.

Pfeiffer reportedly began to brandish a firearm that the 26-year-old homeowner had left at the property. The group initially took photos of the gun and fooled around with it, before a verbal argument began about Pfieffer's sexual history.

"Ruiz was speaking to the other female regarding the argument when Pfeiffer approached Ruiz and pointed the gun at her head and shot her. Detectives say Pfeiffer then shot himself in the head."

The investigation is ongoing and a medical examiner will conduct a formal autopsy.