Four U.S. citizens were shot to death in separate attacks in the border city of Ciudad Juarez, Mexican authorities said Monday.
Chihuahua state prosecutors' spokesman Arturo Sandoval said Edgar Lopez, 35, of El Paso, Texas, was killed Sunday along with two Mexican men when gunmen opened fire on a group standing outside a house.
On Saturday, a 26-year-old U.S. woman and an American boy were slain shortly after crossing an international bridge from El Paso. Giovanna Herrera and Luis Araiza, 15, were shot to death along with a Mexican man traveling with them just after 11 a.m., Sandoval said.
Sandoval said authorities also identified a 24-year-old woman killed Friday inside a tortilla shop as Lorena Izaguirre, a U.S. citizen and El Paso resident. A Mexican man was also found dead in the store.
Sandoval did not provide any information about possible motive in any of the slayings.
U.S. State Department spokesman P.J. Crowley confirmed three of the killings but did not have any information about Izaguirre. He said officials had been in touch with the victims' families but offered no other details.
Ciudad Juarez has become one of the world's deadliest cities amid a turf war between the Sinaloa and Juarez drug cartels. More than 2,000 people have been killed this year in the city, which is across the border from El Paso.
Also Monday, federal police said they arrested a U.S. man accused of being a member of the Aztecas gang, whose members work as hitmen for the Juarez cartel and operate on both sides of the border. Angel Martinez, 24, was arrested Saturday in Ciudad Juarez when he was traveling with another gang member, the department said.
Elsewhere, three city police officers were gunned down early Monday in a drive-by shooting as they patrolled the heart of Acapulco's upscale tourist district, authorities said.
Another officer was wounded, according to a statement from the Public Safety Department in southern Guerrero state, where Acapulco is located.
The officers were patrolling the Puerto Marques area around 1 a.m. when they were ambushed by suspects shooting assault rifles from inside a car, police said.
Violence continues to escalate in the Pacific resort city, days after Mayor Jose Luis Avila Sanchez warned people to stay indoors after dark. Ten other people were killed between Sunday and Monday around the area. Authorities also were trying to determine whether a burned corpse found in a car was the body of a Canadian businessman who disappeared last week.
Meanwhile, the remains of seven people were found Sunday in a mass grave in Nogales, on the Arizona border. Mayor Jose Angel Hernandez said a family walking near the site noticed what appeared to be part of a body sticking up in a riverbed. Officers recovered six bodies and a severed head in the grave. A seventh headless body was found nearby.
In the border city of Tijuana, state police seized more than 14 tons (13 metric tons) of marijuana in two vehicles at a house in the same neighborhood where gunmen killed 13 people at a drug rehab center 10 days ago.
50 bullets hit car with Texas plates in Juárez
By Daniel Borunda
El Paso Times
Three people riding in a BMW with Texas license plates were killed in a shooting during the weekend in Juárez.
Chihuahua state police identified the victims as Guillermo Araiza Hidalgo, 23, Luis Carlos Araiza Hidalgo, 15, and Giovanna Herrera, 26.
A spokesman for the Chihuahua attorney general's office on Sunday did not have information on whether any of the victims were El Paso residents or U.S. citizens.
Police said shooters fired 50 rounds from 9 mm and .223-caliber weapons, peppering the black 2001 BMW X5 with bullets during an assault late Saturday morning on the Juárez-Porvenir road. The vehicle was being driven by Guillermo Araiza. All three died at the scene.
In other news, a Juárez university student is in stable condition and expected to recover after being shot in the abdomen by Mexican federal police during a protest Friday, university officials said.
Jose Dario Alvarez Orrantia, 19, is in his first semester studying sociology at the Autonomous University of Ciudad Juárez.
The shooting occurred during the "March Against Death" to protest the violence and the "militarization" of Juárez.
University officials condemned the shooting in an open letter to Mexican President Felipe Calderón and other government leaders.
"At this time, the university community is offended by these acts of violence that are in addition to other acts in which we have been victims. In none of these cases have the corresponding authorities made significant advances in their investigations," the letter stated.
Federal police said in a statement that the shooting occurred when officers -- who were responding to a shooting nearby -- fired warning shots into the air after running into protesters, some of whom were masked. Two police officers were detained. An investigation continues.