(CNN) -- Dozens of 911 calls released Wednesday by the Carson City, Nevada, Sheriff's Office capture the horror of a mass shooting at an IHOP restaurant.

In one call, a woman sobs as she tries to give the location of the shooter who fatally shot four others before he killed himself in the parking lot.

Others seemed to be left almost speechless by the trauma as they give descriptions and accounts.

"Hurry send ambulances," one woman pleads. "There are people dead."

A total of 11 people were shot Tuesday, Carson City Sheriff Ken Furlong said. They included five uniformed Army National Guard members and six civilians.

Three Guard members, a civilian woman and suspect Eduardo Sencion, 32, were killed.

Authorities were investigating the motive Wednesday. Family members told authorities that Sencion had a history of mental problems dating back to age 16, a law enforcement official said.

Sencion was carrying an assault rifle and a pistol when he went into the IHOP Tuesday morning, Furlong said.

Ralph Swagler, owner of the nearby Locals Barbecue, told 911 that the shooter, who wore a red shirt and black pants, was carrying automatic weapons.

"Now he is coming back outside with a gun," Swagler said. "He is shooting people in the parking lot!"

At that point, the businessman yells for his son to get out of the way. A burst of gunfire is then heard outside the IHOP.

"He is shooting at us now," said Swagler, who declined to speak Wednesday with CNN about the incident. "Automatic weapons. He is shooting at everybody."

A second assault rifle was found in Sencion's vehicle, according to authorities. Only the assault rifle he carried was fired, the sheriff said.

An IHOP customer talked with 911 operators as he looked inside the restaurant's window after the rampage.

"Oh my God, we've got (expletive) people down."

Sencion, who had no prior criminal history, continued firing in the restaurant's parking lot after shooting the IHOP patrons. Four nearby businesses were hit by gunfire, Furlong said.

Emergency operators remained poised during the barrage of 911 calls. "We've got help on the way," they assured eyewitnesses.

"It was crazy," said one witness calling from IHOP. "It was like a nightmare."

Furlong said he was the second person to arrive on the scene Tuesday morning. He held a woman shot in the head.

"The scene was horrific. It's something that I've never experienced before," the sheriff said. "It looked like a bloodbath, wall-to-wall carnage."

Investigators are trying to determine whether Sencion obtained the AK-47 used in the shooting lawfully.

The released calls include conversations between law enforcement personnel, who are told they need to be on the lookout for possible additional shooters. Sencion acted alone, authorities learned.

In one call, an officer is asked if more assistance is needed.

"At this point we have the scene under control," was the reply.

CNN's Thelma Gutierrez contributed to this report.