A Mexican lawyer who has represented some of the country's best-known drug suspects was stabbed to death outside his home, authorities said Saturday.

Americo Delgado was ambushed Friday evening by at least three men in the city of Toluca, an hour or so outside Mexico City, police said. Authorities did not identify a possible motive.

Over the years, Delgado, said to be 81, has represented a number of prominent drug figures, including Tijuana crime boss Benjamin Arellano Felix and Jesus Amezcua, one of the so-called "methamphetamine kings."

Most recently, Delgado represented Alfredo Beltran Leyva, a suspected kingpin from the northwestern state of Sinaloa who was arrested by Mexican authorities in January 2008. Beltran Leyva's group was once allied with Mexico's most-wanted drug suspect, Joaquin "El Chapo" Guzman, but the arrest ignited vicious fighting between the two factions.

Delgado's slaying was the second this month of an attorney who has represented high-profile drug suspects. Silvia Raquenel Villanueva, a lawyer in the northern city of Monterrey, was gunned down Aug. 9 at a crowded market there, in what appeared to be an execution-style attack.

Villanueva's clients included Carlos Resendez Bertolucci, a member of the Gulf cartel whose testimony helped convict kingpin Juan Garcia Abrego on trafficking charges during the 1990s.

Mexico's drug underworld has become increasingly violent amid a government crackdown that has exacerbated rivalries between trafficking groups. More than 11,000 people have been killed in drug-related violence since President Felipe Calderon launched the offensive in December 2006.

Mexico does not have open, U.S.-style trials; the work of defense lawyers in drug cases here tends to be behind the scenes. Lawyers file motions challenging the legality of arrests or seizures, seek court injunctions to free clients from jail and fight extradition requests. But their work carries risks because it puts them close to suspects and can antagonize rival traffickers.

Delgado handled dozens of drug cases in his long career. In recent years, he worked on behalf of Arellano, who was arrested in 2002 and convicted in Mexico on drug-trafficking and money-laundering charges. Arellano has fought extradition to the United States.

Delgado, listed by the Reforma newspaper as 81, was honored by the National Autonomous University of Mexico and a national lawyers group for a legal career spanning more than half a century.

ken.ellingwood@latimes.com