Published: May 20, 2010 10:42 PM EDT
Updated: May 20, 2010 11:01 PM EDT

Cape Coral, Fla - New details emerge in the death of an elderly Cape Coral couple.

The two were found dead at their home SE 30th Street Wednesday night.

Thursday, investigators said the couple died from carbon monoxide poisoning.

"I can not believe it," said one stunned neighbor.

Late Wednesday night into Thursday afternoon crime scene tape stretched across the home of 81 year old Rogelio Gonzalez and his girlfriend, 75 year old Shannon Johnston.

The two were found dead by Gonzalez's brother Wednesday night.

"That's so sad," a neighbor said.

Cape Coral Police said the two died from an accidental carbon monoxide poisoning.

According to police, the couple inadvertently left their van running inside the garage.

Eventually they realized it, turned the van off and opened the garage door for ventilation.

But it was too late.

The poisonous gas had already spread into the home.

It's fast and lethal.

"It is quick. You'll get dizzy, headaches. confusion. comatose. Then of course death," said Rob Blasetti, a Battalion Chief with the Cape Coral Fire Department.

Rescue crews say the amount of carbon monoxide found in the house was so high, that one of the detectives on scene had to go to the hospital to be treated after being inside the home for just short time.

That investigator is okay.

Blasetti says this accidental death is warning for others to be careful.

"You can succumb to it and not even know it. You just fall asleep," he said about the odorless and clear gas.

Blasetti adds if you're ever in a situation where you suspect carbon monoxide in your home, call 911 immediately.

"Call us. We have monitors to check the levels. We have fans to ventilate the house. And of course get out of the house," he said.

Carbon Monoxide deaths are preventable.

To help detect levels in your home, get a carbon monoxide detector.