Four men were convicted Thursday of the murders of 15 young people attending a birthday party last year in Ciudad Juarez, a border city in northern Mexico.

Juan Alfredo Soto Arias, Aldo Fabio Hernandez, Jose Dolores Arroyo Chavarria and Heriberto Martinez were found guilty of the killings on Jan. 31, 2010.

The verdicts were read in the presence of relatives of some of the victims.

The four men will be sentenced on July 11 for the killings in the Villas de Salvarcar section of Ciudad Juarez, located across the Rio Grande, from El Paso, Texas.

Prosecutors called 17 witnesses, including massacre survivors, during the trial, which started on June 20.

Soto Arias, Hernandez, Arroyo Chavarria and Martinez were among the 20 gunmen who attacked the partygoers, a survivor told the court.

The defense, which also called a number of witnesses, contended that Martinez and Hernandez were attending a party at the time that the massacre occurred.

The federal government's "Todos Somos Juarez" program, which was implemented in February 2010 in response to the massacre, rolled out 160 projects dealing with business, jobs, health, education and social development within 100 days.

The projects were designed to rebuild the border city's society and promote co-existence among residents.

The federal government budgeted 3.38 billion pesos (about $277 million) for the program in Ciudad Juarez, with the funds mostly going toward security, education, sports, health, social development and jobs.

The border city's residents, however, have seen few improvements and many projects have failed to live up to expectations, grassroots groups say.

Since the birthday-party massacre, Juarez has been the scene of several other attacks targeting young people.

Gunmen killed 15 other teenagers on Oct. 23 at a house in the border city's Horizontes del Sur neighborhood.

Seven young men were gunned down on Jan. 23 while playing soccer at a recently inaugurated park built as part of the Todos Somos Juarez program.

More than 3,100 people died in drug-related violence in Ciudad Juarez in 2010, and the killing has not slowed this year, with more than 1,100 people murdered in the border city.

The violence is blamed on a war for control of the border city being waged by the Juarez and Sinaloa cartels with backing from hitmen from local street gangs.

At least 14,000 "armed criminals" are in Ciudad Juarez and Chihuahua city, working for the drug cartels that are fighting for control of smuggling routes into the United States, Chihuahua state Attorney General Carlos Manuel Salas said last month.

Some 5,500 of the armed criminals operating in Ciudad Juarez belong to Los Aztecas, a gang that works as the armed wing of the Juarez cartel, while the rest work for the Sinaloa cartel, Salas said.

About 40,000 people have died in drug-related violence since President Felipe Calderon declared war on Mexico's cartels shortly after taking office in December 2006.