A 2-year-old boy has become the second victim, along with his mother, to die from injuries suffered in a Wednesday morning fire in St. Paul, while two others badly burned in the blaze are expected to survive, family members said.

William Mangan died overnight, hours after his mother, Tiffany M. Alexander, died in the blaze in the Alexanders' apartment at 1035 Arkwright St. N.

Alexander's mother and William's grandmother, Thereza "Tess" Alexander, 47, also suffered serious injuries, along with another 2-year-old grandson, Gabe.

Thereza Alexander's sister, Lisa Wright, said that she is in a medically induced coma and does not know that her daughter and grandson are dead.

"Thereza loved the kids, and she's going to be devastated when she finds out what happened to her daughter and the kids," Wright said. "She should pull through just as well as Gabe if there's no infection."

Wright said one of her nieces was at Regions giving birth the same day the family was transported there for their fire injuries.

Glen Stubbe, Star Tribune
Gallery: One dead, three injured in St. Paul fire

"We're just doing the best we can," she said.

Neighbors and firefighters who rushed to the aid of the family Wednesday morning said they were perplexed that no one was able to escape the blaze, which remains under investigation.

"I don't know why the people couldn't get out on their own," said St. Paul Fire Marshal Steve Zaccard. "9:20 in the morning is when we got the call, I don't know why they couldn't escape and what happened here."

The Ramsey County medical examiner's office said Thursday that it has yet to reveal a cause or manner of death for either Tiffany Alexander or her son. Toxicology test results are pending.

Marti Capaul, a cousin to the Alexanders, confirmed that William has died since the blaze. Capaul added that Tiffany's daughter, Destinee, was with her father at the time and was not injured. Neighbors initially thought the girl, 3, was in the apartment.

"Our family is pulling together to try to get through," Capaul said Wednesday. "I know that Tess' and Gabe's burns were bad, but I don't have more details."

Authorities haven't said what may have caused the fire in the Alexanders' apartment at 1035 Arkwright St. N., but police taped off the block Wednesday morning and called it a crime scene. Zaccard said firefighters were able to quickly extinguish the fire in the first-floor unit, and that it's too early to identify the cause.

"We're working with the St. Paul Fire Department to determine whether there was anything criminal involved in this tragedy," said police spokesman Steve Linders.

Police are not calling it a homicide, Linders said, adding and that he was not aware of any arrests in the case. Nicole Shelton said police questioned her and others Wednesday, including an ex-boyfriend Tiffany Alexander broke up with about a week ago.

Tiffany Alexander and the man dated for about three years, Nicole Shelton said. He is William's father, and was apparently at the family's apartment Tuesday when an altercation broke out, according to Nicole Shelton.

The man arrived at the fire scene in the late morning, screaming that his "wife" had died.

Fanchon Shelton said she first knew something was wrong Wednesday when she looked out her window and saw black smoke billowing above the second-story building. She ran downstairs and banged on the Alexanders' door. No one answered, so she twisted the door knob.

"It opened right up," she said of the door, "and all the smoke came out but I didn't hear anything."

Fanchon Shelton ran back upstairs to evacuate her 3-year-old son, her sister and her 3-year-old niece. Thereza Alexander would typically be up and ready to leave for work about that time, Fanchon Shelton said.

"They were all in their sleep, that's what I don't understand," she said. "The whole house was asleep."

When Nicole Shelton fled downstairs, she saw a burned and soot-covered Thereza Alexander.

One woman died and three others, including two children, were severely injured in the fire at a St. Paul apartment building Wednesday morning. The cause of the fire, and why the four could not escape, is currently unknown.

"Tess, her nose — everything — was black," Nicole Shelton said. "And she's just looking at me and it didn't seem real. It didn't. She was burned so bad.

"She told me, 'Tiffany and the kids are still inside,' and she fell."

Nicole Shelton called 911. She later recalled not hearing any smoke alarms going off although alarms had recently been installed. Fanchon Shelton said the building is equipped with smoke alarms and fire extinguishers, and is well maintained.

Robert Humphrey, a spokesman for St. Paul's Department of Safety and Inspections, said the building was last inspected in February 2016, and did not have any fire code violations. Although inspections are a "snapshot" in time, he said, the building was in "good standing" with the city, and was due for another inspection later this year.

The family has set up a GoFundMe page for Tiffany Alexander's family at https://www.gofundme.com/helpalexanderfamily.

Star Tribune staff writer Paul Walsh contributed to this report.

Chao Xiong • 612-270-4708 Twitter: @ChaoStrib