DEL RIO, Texas -- Authorities said it is the first case of a Mexican city official being gunned down on this side of the United States border with Mexico.

Investigators said Mario Espinosa Lobato was assassinated in the driveway of his home in Del Rio in September, KSAT 12 News reported.

The Val Verde Sheriff's Office, Texas Rangers, FBI and Mexican authorities are all investigating the slaying.

"We are handling this as a contract killing -- a murder-for-hire situation," said Larry Pope of the Val Verde Sheriff's Office.

Lobato was a member of the Ciudad Acuna City Council and a former law enforcement officer, who was known to take on drug smugglers and politicians alike.

"A lot of people in Mexico would get threats and they would come to him for advice on threats they had received," said Pope.

Authorities said Lobato's bodyguards couldn't cross into the U.S. because they were assigned to him by the Mexican government.

Investigators said perhaps whoever ambushed him in Del Rio knew he no longer had protection.

Authorities said the fatal shooting also might have been a kidnapping gone bad. Police said Zeta drug ring enforcers already had tried to kidnap Lobato two years ago in Acuna.

"So it actually made him work more and help more and be more of a spokesperson," said the victim's daughter Edith Trevino.

A Del Rio school board member, Trevino said she tells her children that their grandfather was like a soldier in battle.

"Papa Mario was that way, he was a hero for the poor people," said Trevino.

Among his charity work, Lobato's family said he would build more than a dozen homes a year for Acuna's families using his own funds.

His family said they hope to keep his legacy alive.

"We just don't know how much we will miss that strength," said Trevino.

Trevino shared that her father used to say, "When I die, I'm going be the kind of person people are going to remember."

Stay with KSAT 12 News for the latest updates in this developing story.