The fire happened around 1:30 Saturday afternoon on the 1100 block of West 5th Street.
65-year-old Jose DeJesus, who is disabled, died on the third floor.
Authorities say Johnny Williams, who lived on the first floor of the apartment, intentionally set the fire. He now faces murder and arson charges.
Firefighters rushed to the scene Saturday afternoon to find heavy smoke and fire. They say DeJesus was trapped in his third floor apartment.
"I knew it was hard for him to get out so I was just crying trying to call but it happened so fast, the fire went like that," said Tamara Howard.
Family members Williams say had been suffering from dementia and depression.
They say he wouldn't let anyone inside so they called police.
"We don't know what was in his mind, what happened over here, but all we know is he was screaming and hollering he was trying to kill himself," said Nathan Williams, step-son.
"Our family is deeply sorry to the family that lost their loved one for what happened but unfortunately with elderly dementia patients sometimes they slip under the radar," said Taneka Williams, granddaughter.
A resident from a second floor apartment was injured but able to escape.
The fire heavily damaged 70-year-old Mary Berry's home next door. Berry says she has lived here for 41 years.
DeJesus was also a longtime resident who lived here for decades.
"Every day taking the kids to school, I would say 'Jose' and he would say 'Hey' and I would keep it moving. He was just always at the window," said Damaris Zayas.
Another resident was inside the building at the time but escaped with non-life threatening injuries.