Albuquerque (AP) — Police were searching Monday for at least two more men suspected of carrying out a weekend robbery at a crowded Denny’s restaurant that left one woman dead.

At least four masked men armed with handguns and rifles ordered a manager to open the cash register Saturday morning and then took an undetermined amount of money. Stephanie Anderson of Albuquerque, who worked as a cook at the restaurant, was killed during the holdup.

Pablo Ortiz, 32, and Marvin Lopez-Aguilar, 22, are being held without bond on charges of murder, robbery, 40 charges of kidnapping, five counts of child abuse and tampering with evidence. The child abuse counts are because five children were at the restaurant during the robbery.

Police Chief Ray Schultz announced during a news conference Monday that investigators have identified 25-year-old Francisco Melgar of Albuquerque as one of the other men involved in the robbery. A warrant has been issued for his arrest.

The fourth suspect has yet to be identified, the chief said.

Investigators believe the group is linked to a number of robberies that have occurred over the last month in Albuquerque, including at least three robberies at restaurants. They also believe that Ortiz and Melgar are involved with MS-13, a gang founded by Salvadoran immigrants.

The men had the numbers “503” shaved into their heads. The numbers — the telephone country code for El Salvador — are commonly worn by MS-13 members.

Schultz said Albuquerque police are working with the U.S. Marshal’s Service, U.S. Immigration and Customs Enforcement and the U.S. Border Patrol to apprehend Melgar and identify and capture the fourth suspect.

Melgar is described as having a tribal tattoo on his left arm, standing about 5-foot-5 and weighing 155 pounds. Police could not say whether Melgar was still in the Albuquerque area.

Schultz stressed that the investigation was ongoing and more charges could be filed if the group is found to be connected with other robberies.

Schultz said the case highlights the need for state statutes to include definitions for gangs and gang members. Without the definitions, investigators have a hard time tracking the extent of gang problems in New Mexico communities.

“If nothing else, this case should help us be successful in the next legislative session in getting over that one hurdle,” he said. “And without that hurdle, I think we’ll be able to do many other good things to help create statutes that effectively go after gang members and the crimes they commit.”