One couple vanished on the way to a play at a local theater. Two brothers disappeared on the way to a restaurant. Many victims were seen by witnesses being stuffed into official-looking vehicles by assailants wearing Mexican police or military uniforms.

"It's an incredible, horrible thing," Jaime F. Hervella, who lives in El Paso and is a founder of the Association of Relatives of Disappeared Persons, said today in response to the discovery of suspected graves at two ranches near this border city. "[The bodies] have got to be ours."

U.S. and Mexican law enforcement officials today continued excavations in at least two of four sites that authorities believe could contain the remains of dozens of Americans and Mexicans who have vanished during an unsettling spate of crimes near the international border shared by Ciudad Juarez and El Paso.

Until Monday, when authorities announced the investigations of possible burial sites, the families of nearly 200 people who have disappeared over the past five years searched for clues with little assistance from either Mexican or U.S. law enforcement authorities, relatives said. Now, while no victim has yet been identified, there's hope that the mystery may be near an end as authorities reported finding what could be human remains at one of the sites.

"This is the closest we've gotten to something that is real," said Claudia Sanchez, 21, whose parents vanished May 24, 1994, while waiting to enter a Ciudad Juarez theater. "I will suffer in some ways, but it will be a relief to know they're there, that we have a place to go and take flowers and pray for them."

Many, but not all, of the people who disappeared in the Ciudad Juarez-El Paso area are believed to have had some association with the drug trade. Many were thought to have been abducted by corrupt Mexican law enforcement and army officials who may have been on the payroll of drug cartels, according to family members and human rights organizations.

"In many cases someone saw them being taken," said Hervella. "There was a lot of precision and weaponry and dark, funeral-like Suburbans."

The names of 196 missing people compiled by the association cover a broad spectrum of lifestyles, backgrounds and professions: U.S. citizens, Mexican citizens, Mexican law enforcement agents, informants, drug traffickers, low-level drug peddlers, restaurant owners, an auto mechanic and Sanchez's father--who once served in the U.S. Navy and was a communications whiz.

Although Ciudad Juarez, the center of operations for Mexico's most powerful drug cartel, has always had high murder rates along with occasional disappearances, the rate at which individuals vanished over the past five years is staggering, according to groups monitoring the crimes. And while activists conceded that many of the disappearances may have been the work of cartels seeking revenge on those who betrayed them, they noted a telling difference that they say points to the involvement of law enforcement agents.

"The bodies [of those] killed by the mafia are always found," said Victor Clark of the Tijuana-based International Commission on Human Rights. "It's their way of sending messages."

In Ciudad Juarez, by contrast, the victims simply disappeared and only now may be found buried beneath the isolated and harsh desert surface--possibly the work of abductors trying to hide evidence. Law officials may have been involved not only as corrupt agents of the drug cartels but also as vigilantes targeting narcotics traffickers, activists say.

"The families always hoped that their relatives would come back alive, that they were being held in clandestine military jails or that they were in witness protection programs," said Alberto Medrano Villarreal, a lawyer for families of the disappeared and president of the Ciudad Juarez Bar Association.

"As a lawyer this is a terrible discovery because you suppose that you live in a just society where even the worst criminal, even the most hardened drug trafficker has the right to a trial," said Medrano. "We had suspected that police were involved in the disappearances. . . . Our society can't just say, 'He was a narco-trafficker and it's good that he was executed.' If judges can be wrong, the triggermen can be wrong, too."

Ramon Alonzo peered through the metal gates of a small desert ranch today, searching for the answers he has sought--and dreaded finding--in the 30 months since his older brother, Jose, disappeared after several men came to his Juarez house to discuss a car they wanted the auto mechanic to repair.

His brother, wife and six children never heard from Jose, then 33, again.

"We just want to know what happened," said Alonzo, 36, echoing the weary sentiments of most of the families.

But it could be weeks before identifications are made because of the advanced state of decomposition of what could be human remains found today by U.S. agents and Mexican federal police wearing black uniforms and ski masks to hide their identities.

Saul Sanchez Jr. was 39 when he disappeared in 1994 outside the theater with his wife, Abigail, 38. The U.S. Navy veteran and engineer had invented a device that could track cellular phone calls, which he sold to the Mexican federal police for use in drug investigations, according to his family.

His father, Saul Sr., said in a telephone interview today that he had tried to persuade his son to move out of Ciudad Juarez and to El Paso because he feared the federal police's reputation for corruption. He remembers the day he hectored his son: May 17, 1994. "A week later, he and his wife had gone to the theater. Someone from the Mexican federal police said he had the tickets for the theater, and he wanted to meet them there," said the older Sanchez. "That was the last time he was seen."

Since then, Sanchez has nagged the FBI to investigate his son's disappearance. "The FBI doesn't care. They have never cared about anything to do with this," he said.

Esperanza Gomez de Ontiveros, 56, a retired teacher, has had similar experiences with Mexican authorities since the disappearance of her son, Victor Hugo Ontiveros Gomez, on Sept. 2, 1996. He had been a shooting and firearms instructor for the Chihuahua state judicial police academy.

"Since my sons worked for the state police I thought we would get a lot of institutional support, but the authorities haven't told us anything," said Gomez. "We've been like this for three years. We don't know what they've found in those graves. I just hope something comes out of this. You're just waiting to hear anything, that they have found a grain of sand, anything to be able to say, 'There he is.' "

Staff writers Paul Duggan in El Paso and Lorraine Adams in Washington and researcher Garance Burke in Mexico City contributed to this report.

CAPTION: Ramon Alonzo holds pictures of people who disappeared, including his brother.

CAPTION: Masked Mexican policeman directs traffic entering ranch where authorities are investigating a possible grave site.

CAPTION: Claudia Sanchez displays the last photograph she has of her parents.