Acting on a tip, Philadelphia police captured 25-year-old Carlos Rivera in the 1800 block of Russell Street on Monday night.
Rivera was taken into custody for an armed robbery which occurred on March 1st in the 500 Block of Adams Avenue.
Police then also charged him with the murder of his girlfriend, 35-year-old Atlanta Deveney, and her son, 12 year old, Elijah Rosado, that occurred on Saturday, October 5th on the 4600 block of Howell Street.
Their bodies were found in a closet of the first floor apartment.
Police revealed Monday that Deveney appears to have suffered trauma to her head. However, the cause of death is undetermined at this time. Elijah suffered stab wounds to his chest and neck.
It is believed the boy may have been murdered while attempting to protect his mother.
Police say Rivera has a long history of domestic abuse.
However, despite the armed robbery and history of abuse, Deveney allowed Rivera to move in with her and her son three months ago in that apartment. Police say she did not get a protection from abuse order.
Police say it was Rivera that was outside the apartment as the fire was burning telling people not to call police because he had it under control.
The fire happened just before 9:00 a.m. Saturday on the 4600 block of Howell Street.
As the building filled with smoke, neighbors started banging on doors when they encountered a man, later identified as Rivera, who asked for a fire extinguisher but had another disturbing request.
"He said, 'Don't call the police, we'll handle it, we'll handle it.' Evidently that was from the apartment where the bodies were found and he wouldn't let me near the house with a fire extinguisher," said Mary Pommer.
Neighbors called 911 anyway. Firefighters discovered the bodies of the woman and her 12-year-old son in the closet of their first floor apartment.
The fire marshal quickly determined it was a case of arson.
Action News has learned the young mother and son moved in a few days ago.
"The little boy had been walking his dog up and down the sidewalk every day," said Pommer.
George Kelly, the building's owner, says Atlanta Deveney was in the process of being evicted from another one of his apartments and was going to stay here temporarily.
"The caseworker called me and asked me if I could find them a place for a few days or a month," said Kelly.
Crime scene investigators searched the area for clues and questioned people who knew the victims.
Meanwhile some neighbors like Nina Ervin were able to move back into the building despite some smoke damage.
"It's horrible. I wouldn't wish that on anyone, I feel really horrible for the little boy," said Ervin.
A memorial for the victims has been set up next to some debris from the fire.
The Associated Press contributed to this report.