Martin Quinteros Chavez knew his father had not shown up for work Tuesday morning, and he worried his stepmother might be having trouble from a recent back surgery. He called again and again but got no answer, so he headed to their Oxon Hill house.

The brick home where five Salvadoran immigrants lived was quiet, and there was a faint odor of gas, Chavez said. In the bed in the master bedroom, he found the first body. On the floor in another room, he found the second.

In total, authorities said, five people were dead — apparent victims of carbon monoxide that had leaked into the home from “rusted and separated” exhaust pipes on a natural gas furnace. Chavez said he found the bodies of his stepmother’s sister and a family friend. He said he left in fear — dialing 911 from his cellphone — before firefighters arrived and pulled out the bodies of his father, stepmother and another family friend.

Prince George’s County Fire/EMS Chief Marc Bashoor said that although homicide detectives and fire investigators are still reviewing the incident, “there is no indication of anything other than a tragic loss here, a tragic accident.” He said carbon monoxide, which has no odor, probably killed those inside the home rapidly.

Chavez and other family members and friends said that they had been in the house or seen those who lived there Monday night and that nothing had seemed amiss.

“The reality is these people were affected very quickly by a large quantity of carbon monoxide,” Bashoor said.

On Tuesday afternoon, dozens of family members and friends of those killed descended on the 700 block of Shelby Drive, crying and hugging one another. Most said they came from two pentecostal churches — Iglesia Pentecostal Torre Fuerte in Northern Virginia and Tabernacle de Restoracion in Oxon Hill — where Chavez’s family and the home’s other occupants were active.

Authorities identified those killed as Oscar Chavez, 57; Sonia Maribel Leiva, 54; Nora N. Leiva, 57; Francisco Javier Gomez Segovia, 33; and Nelson Enrique Landaverde Alas, 44. Authorities and family members said Chavez and Sonia Leiva, who also went by Sonia Chavez, were husband and wife; Nora Leiva was Sonia’s sister, visiting from Chicago to care for Sonia after her recent surgery; and the other two men were family friends.

All the occupants were from El Salvador, friends and family members said. Jose Rosales, 42, a family friend, said Segovia and Alas had wives and children living there.

The residents were also very involved in church life, friends and family members said. Rosales said Segovia preached around the region; Angel Diaz, 34, another friend, said Alas sang in the church band.

“It’s hard,” Diaz said. “He was real nice . . . like family.”

Yamileth Coreas, Sonia Leiva’s daughter, said her mom worked at a Giant grocery store bakery and “came to this country to live a better life.” Martin Chavez, Oscar’s son and Sonia’s stepson, said his dad owned the home and worked in construction.

Chavez said he first worried something was wrong when he tried to call his parents just after 6 a.m. Tuesday — part of a daily ritual to make sure that his stepmother was recovering well from her surgery. He said he soon learned his father had not gone to work that morning, so he went to the house.

Chavez said that when he saw the bodies, he rushed out. He said he called 911, assuming his family and friends had been robbed and slain.

Bashoor said firefighters arrived and found carbon monoxide levels of 140 parts per million near the home’s front door — far above the 0 to 5 parts per million that is considered normal and the 30 parts per million that can be fatal over time. And as firefighters went deeper inside the home, Bashoor said, they found carbon monoxide levels as high as 560 parts per million.

All five people were pronounced dead on the scene, Bashoor said. He said firefighters pulled a small dog from the home and that it was being treated.

Fire officials across the region and the country have long warned of the dangers of carbon monoxide. The toxic gas drew special attention locally in 2010, when at least 19 people, many running gas-powered generators inside their homes, were hospitalized for carbon monoxide poisoning during and after a winter storm, and three people died in a separate incident involving a generator. A Centers for Disease Control and Prevention fact sheet says that more than 400 people die from accidental carbon monoxide poisoning each year.

In Tuesday’s case, fire investigators think an exhaust pipe — one designed to ventilate toxic gas that is produced from the combustion of natural gas in a furnace — was broken “due to normal wear and tear,” authorities said. Bashoor said temperatures in the area dipped between 32 and 40 degrees Monday night.

Chavez said that he visited his parents’ home Monday night and that the temperature seemed normal, if a bit cold. He said he did not detect any gas or feel any symptoms normally associated with carbon monoxide poisoning.

Bashoor said that in the past two months, fire officials had received four calls for suspected carbon monoxide leaks in the neighborhood surrounding Shelby Drive. That is not unusual, Bashoor said, for a group of homes constructed around the time of World War II.

Still, Bashoor said, firefighters went door to door after those calls to warn residents of the dangers of carbon monoxide poisoning, and they planned to continue that effort across the county in the wake of Tuesday’s incident in hopes of preventing more deaths.

Staff researcher Magda Jean-Louis contributed to this report.