The FBI has begun a preliminary investigation into whether a local police officer violated the civil rights of a 64-year-old man who was shot and killed in his home during a botched drug raid.

Shortly before midnight on Aug. 9, the El Monte Police Department's Special Emergency Response Team, armed with a search warrant, stormed a modest blue and white stucco home in Compton as part of an ongoing drug investigation. Officers shot locks off both the front and back doors, threw a flash-bang grenade onto the ground behind the house and shot a "diversionary device" into a back room for illumination.

Minutes later Mario Paz, a grandfather who had been sleeping with his wife in the bedroom of their home of more than 20 years, was dead from two gunshot wounds to his back. Outside, officers were interrogating the four other residents of the house, including his handcuffed widow, wearing only her panties and a towel draped over her chest.

Officers did not file charges against any of the residents.

Police had entered the right house, the address specified in the warrant for a nighttime, "high-risk entry." The warrant said they expected to find marijuana, drug paraphernalia, money or guns. Officers seized three handguns, a .22-caliber rifle and $10,000 cash. The family said they kept the guns for protection in their high-crime neighborhood. The cash, they said, was their life savings, recently withdrawn from a bank in Tijuana, Mexico. The family has the withdrawal slip.

Police said they did not find any narcotics or drug paraphernalia.

Police said they had gotten the address for the Paz residence off the vehicle registration and other documents belonging to Marcos Beltran Lizarraga, a drug suspect.

Brian Dunn, a lawyer from Johnnie L. Cochran Jr.'s firm who is representing Paz's family, said that Lizarraga lived next door to the Pazes during the 1980s and that the family sold him the car six years ago. He occasionally received mail at their house. Dunn said that the police should have at least found out who was living in the house before raiding it.

Assistant U.S. Attorney Mike Gennaco, who has been tracking the case, said his office asked the FBI to open an investigation last week. "What we have right now is a criminal investigation into the individual officer's actions," he said.

An FBI spokeswoman confirmed that an agent has been assigned and a preliminary investigation is underway. Once completed, it will be forwarded to the Justice Department, which decides whether to prosecute.

This is the latest fatal shooting by local police that has drawn public outcry and federal scrutiny over whether officers used excessive force. In a well-publicized incident last December, four Riverside officers shot African American teenager Tyisha Miller a dozen times after responding to a 911 call about an unconscious woman in her car. Those officers have been fired. In May, Los Angeles police officers shot a mentally ill homeless woman, Margaret Mitchell. That incident is still under investigation by the Los Angeles County Sheriff's Department.

The Sheriff's Department, which routinely investigates officer-involved shootings, has provided three explanations for why officers fired at Paz.

At first they said the El Monte officers believed Paz was armed. Later they said that he was reaching for a gun. The latest statement said officers saw Paz reaching for a drawer where guns were found.

"From the family's standpoint that's just another justification for the empty killing of an innocent man," said Dunn. "Any time you have a shooting of an unarmed man who is totally clean, the police have to justify their actions, they have to justify the homicide."

El Monte Assistant Police Chief Bill Ankeny said that so far only the family's side of the incident has come out and he hopes the sheriff's investigation and the federal review will result in the release of information that defends his officers' actions.

"We don't like the picture being painted," Ankeny said.

Although he can't comment specifically on the case because of the investigation and the possibility of a lawsuit by the Paz family, Ankeny said he thinks officers followed standard procedures for this type of raid, which he emphasized was considered "high risk" to officers. Still, he says this was an unfortunate incident.

"Any loss of life, be it police or civilian, is certainly a tragedy," Ankeny said. "They certainly have our sympathy."

El Monte, a suburb east of Los Angeles, has an aggressive anti-drug program. According the police department, officers often serve warrants in other jurisdictions when they relate to the department's cases. In this instance, El Monte did have the cooperation of the Compton Police Department. The family's attorney said the family wonders why law enforcement needs to use such forceful methods to execute search warrants.

"The reason why Mario Paz is dead is the manner in which his house was searched," Dunn said. He described the police entry into the Paz house as a "full-scale, military commando-style raid," which the family initially thought was a home-invasion robbery. "Those kinds of tactics should not be used against law-abiding people," he said.

CAPTION: In Compton, Calif., Maria Durain, right, comforts her mother, Maria Luisa Paz.