A California man who is suspected of killing four people in a series of shootings has been dubbed a serial killer by the Los Angeles Police Department.

Alexander Hernandez, a 34-year-old man from Sylmar, was arrested Sunday on animal cruelty charges and on Tuesday was charged with the fatal shooting of a man in Pacoima and an attempted double murder in West Hollywood, according to the San Jose Mercury.

Hernandez has not yet been charged with three murders that happened on Sunday, though he is a prime suspect.

"Nothing makes a homicide investigator's heart beat faster than realizing he has a serial killer. And that is what this man was," said sheriff's Chief of Detectives Bill McSweeney, The Los Angeles Times reported. "This man is and was a serial killer.... I don't think we will ever have an adequate explanation for these terrible murders. How do you explain anything like this?"

Officers found Hernandez after driving by a house in Sylmar on Sunday and finding two dogs had been killed. Hernandez was charged with animal cruelty in that case and also will be charged with killing 48-year-old Gildardo Morales and firing on a couple in a truck in West Hollywood.

Even though Hernandez has yet to be charged for a string of murders on Sunday, police say they have significant reason to believe he is responsible.

"We anticipate charges will be filed on the three homicides that occurred in the San Fernando Valley on Sunday in the next several days to weeks," LAPD Deputy Chief Kirk Albanese said at a news conference on Tuesday in Los Angeles. "We're very confident of that. We believe we have the right man."

The three victims of the Sunday killings were all in vehicles, and the nature of the crimes would make Hernandez eligible for the death penalty, if he is charged with those crimes. The district attorney's office has not said if it will seek that punishment.