The bodies of one man, aged 42, and two women, aged 31 and 35, were found on Wednesday in a lawyer's office in the Madrid neighbourhood of Usera.
One of the victims had had her throat slit, another had been attacked with an axe and the third had been hit on the head with a blunt object.
Emergency services arrived at the scene after someone called and reported a fire at around 6.30pm. It was then that they discovered the three bodies. The fire was caused by some papers being set alight in the office and was quickly extinguished.
The male victim was found in cardiac arrest, and despite working to revive him for 30 minutes, paramedics eventually pronounced him dead.
“The bodies showed signs of having been burned,” a witness told El País. “They were very red and were black in places.”
The law firm - Euroasia - is that of a Peruvian lawyer who, according to Spanish media, was a public prosecutor in Peru. It specializes in immigration issues.
One of the women has been named as Marisa O. R, 35-years-old, originally from Cuba. She was well known in the neighbourhood and locals gathered outside the law firm in shock on Wednesday night.
“She was always smiling and always said hello to everyone,” a local told El País.
The other two bodies have not yet been identified and forensic experts are currently working on the scene.
Sources close to the investigation told Efe that the two murdered women were employees of the law firm while the murdered man was Ecuadorian and was “most probably a client”.