As Meridian police continued their investigation into an 18-year-old Marine’s death over the weekend, McQuen Forbush’s family and friends gathered Monday night to honor the young man.

The cause of Forbush’s death is suspected to be carbon monoxide poisioning, Meridian Police Deputy Chief Tracy Basterrechea said.

Forbush’s girlfriend found him unreponsive on a bedroom floor at the Sagecrest Apartments on East Overland Road just before 1 p.m. Saturday. Paramedics determined that Forbush had died and rushed the 18-year-old woman — who told first responders that she felt ill — to the hospital.

“They put her in a hyperbaric chamber,” Forbush’s father, Travis, told the Idaho Statesman on Monday. “She was released from the hospital and seems to be doing OK.”

In a hyperbaric chamber, a person breathes 100 percent oxygen at an increased pressure.

Travis Forbush said his son grew up in Farmington, Utah, but finished his last year of high school at Columbia High in Nampa. He graduated in the spring and joined the Marines.

McQuen Forbush was on leave from infantry training at Camp Pendleton in San Diego and was visiting family and friends in the Boise area. The trip was a surprise, his father said.

“His mom didn’t even know he was coming. She saw him for an hour and a half on Friday,” said Travis Forbush, who lives in Farmington.

The grieving father was on his way to the Treasure Valley to attend Monday’s candlelight vigil and to make arrangements to get his son’s body transported to Utah.

He didn’t have much to say about the cause of his son’s death.

“Carbon monoxide overtook him. It took his life,” he said. “We’re looking into that.”

The Ada County Coroner’s Office was closed for the Veterans Day holiday Monday, so no new information was released.

Tony Drost, owner of First Rate Property Management, said Monday that many of the apartments at Sagecrest have carbon monoxide detectors, but he wasn’t sure whether this particular unit did. He said the detectors are installed when tenants move out.

“That’s the most efficient way,” he said. “Safety of our tenants is a No. 1 priority.”

Drost, who has not been given the go-ahead to go into the building since Forbush died, said he heard that it was very warm in the apartment when first responders arrived, so he speculated that a thermostat on the hydronic furnace failed — and kept running.

“I want to get in there and find out what happened,” he said. “I’m planning on going into every single unit and making sure nothing is wrong.”

He said the apartments were built in 2004-05, and each unit has its own furnace. As part of quarterly maintenance, he said, the furnace filters are replaced and other “preventive work” is done.

Drost was meeting with apartment building owners Monday afternoon to discuss, among other things, a letter that will go out to residents about what occurred and what will be done to ensure their safety.

“We feel terrible about what happened, and we want to find out what happened so we can make sure it doesn’t happen again,” he said.

At least 25 states require carbon monoxide detectors in some residential buildings, according to the National Conference of State Legislatures.

Boise Fire Marshal Romeo Gervais said that for new construction, Idaho law requires that carbon monoxide detectors be installed outside bedrooms in dwellings that have fuel-fired appliances or attached garages. That took effect in January 2011.

Katy Moeller: 377-6413