The victims -- three women and a man -- were yesterday celebrating Tomasa Robles' birthday in the garage of a house in Peru's third most populated city, located 500 kilometres north of the capital Lima, when they were shot dead.
Robles, 42, was one of the victims, according to authorities.
Police are investigating the murders in relation to the shooting of another man in the same neighbourhood. Bullet casings from both crime scenes were recovered and taken to a laboratory for comparison.