Mexican authorities have detained a second suspect in the assassination of presidential candidate Luis Donaldo Colosio, widening their investigation beyond the initial lone-killer theory.


Sources close to the investigation said Monday that Tranquilino Sanchez, described by Mexican newspapers as having close ties to the presidential security service, was detained over the weekend after videotape showed him advancing toward Colosio moments before Colosio was shot Wednesday.


"In the footage, Tranquilino Sanchez appeared to have been collaborating with Mario Aburto Martinez," the man charged with firing the fatal shot into Colosio's brain, said Hugo Morales, a spokesman for the Mexican attorney general's office.