SAN ANTONIO, Texas (AP) _ Darlene Garza helped block the deportation of a refugee and with her husband interviewed hundreds of people when she became frustrated with efforts to find the person who killed her brother-in-law.

The search ended May 7 when Carlos Saul Hernandez, 21, was found guilty of the murder of Oscar ''Lenny'' Garza and sentenced to 20 years in prison.

Mrs. Garza began her hunt after Garza, 29, was shot May 17, 1985. He had driven to city's West Side to drop off some workers and to pay a former employee back wages.

Garza was shot four times after an argument with two men, one a Honduran refugee and the other identified only as Saul, witnesses told police. The witnesses said that at one point Garza held up blood-stained money, begging the man not to shoot again.

''At first, we didn't get too involved because it was a police matter,'' Mrs. Garza said.

But frustrated by red tape, she and her husband, Xavier, a letter carrier, visited areas where illegal aliens gather to try to track bits of information.

San Antonio police had no comment on the case. ''We don't feel we have to defend our investigation,'' said Sgt. Paul Buske, a public information officer.

At one point, Mrs. Garza helped block the deportation of the refugee. ''Without him, we didn't have the killer,'' she said. ''So we hit the streets to find evidence to find him.''

She and her husband interviewed hundreds of people within a half-mile of the shooting scene. ''We called people on the phone and we knocked on nearly every door never knowing if the killer might be the one who opened the door.''

Then Mrs. Garza found a woman who knew the refugee and who also told her that the man known as Saul frequently used her house as a mail drop.

Her visit to the house was fruitless. Mrs. Garza went to the house a second time, carrying a .45-caliber automatic pistol in her purse.

In the house, with children playing outside, she met Saul Hernandez.

''I didn't want to shoot him, but I was very aware of the power I had,'' Mrs. Garza said. ''I knew I could just blow him away and walk out and it would all be over. It was a very amazing thing.''

She walked out and drove away. She called police who went to the house and arrested Hernandez.