Ciudad Juarez, Mexico ? Two more Mexican men were in custody Friday in El Paso, Texas, for possible involvement in the killings of women during the past decade in the border city of Ciudad Juarez, Mexican and U.S. law enforcement officials said.

On Thursday, in what was described as a breakthrough in the investigation, the U.S. Embassy in Mexico City announced that another Mexican had been arrested in Denver in connection with the rape and killing of at least 10 women. The man, Edgar Alvarez Cruz, was flown Thursday to El Paso and remained in U.S. custody.

The arrest of two more men could be the most solid indication to date that a serial killer or killers were responsible for some of the hundreds of slayings of women in Juarez and Chihuahua state since 1993, authorities said.