(Reuters) - The FBI will assist local police in investigating the shooting deaths of a woman and her two daughters at a multimillion-dollar home in a gated community of San Antonio in what was initially seen as a possible murder-suicide.

Bexar County Sheriff Javier Salazar said on Tuesday he requested “technical and investigative assistance” from the Federal Bureau of Investigation as his detectives probe the deaths of Nichol Olsen, 37, Alexa Montez, 16, and London Bribiescas, 10, at the mansion.

“We owe it to Nichol, Alexa, London, and their families to find the truth through meticulous investigation. It’s always better to have more tools at our disposal and more eyes on any case,” Salazar said in a written statement.

Salazar has said the investigation would remain open despite a ruling by the Bexar County medical examiner that Olsen’s death from a single gunshot wound to the head was a suicide.

Medical examiners said the two girls had been the victims of homicide. Montez died from a gunshot wound to the head, while Bribiescas was slain by rounds that struck her in the head and neck.

“We can’t just say: ‘This is what the medical examiner says - case closed.’ We’ve still got two murder investigations at this point,” the sheriff told a news conference on Jan. 14.

Olsen’s boyfriend, Charlie Wheeler, 31, called the 911 emergency line on the morning of Jan. 10 to report he had returned to the home he shared with her at about 9 a.m. to find Olsen and the two girls dead upstairs, according to the sheriff’s department.

The San Antonio Express-News reported that Wheeler, who owns the home, told investigators he left the night before after a disagreement with Olsen and stayed with relatives in another city.

Salazar has said Wheeler is a “person of interest” in the case but has been cooperative and was not considered a suspect. The sheriff has said investigators are also looking into the possibility that an intruder unknown to the victims could have killed them during a break-in.