Diana's roommate at the time of the incident was Nicholas Suder, 20. Neighbors and sources who know the family say he is Zapiec's son and the senator's nephew.
No one answered the door when the Daily News made repeated visits to the house yesterday. A plaque bearing the street number was also marked SUDER ZAPIEC, and two campaign signs for Tartaglione were in the window.
Nicholas Suder and Margaret Zapiec are listed as registered voters at the address.
According to city records, Suder makes $30,000 per year as a "trades helper" for the Office of the City Commissioners, which had been chaired for decades by legendary city politician Marge Tartaglione, Tina's mother.
Attempts to reach Suder yesterday were unsuccessful.
In a statement, Sen. Tartaglione said Diana "recently had a falling out with his family over some personal problem. At that time, he asked Nicholas Suder for a place to stay until he got on his feet. Nicholas Suder fully cooperated with authorities and was home asleep at the time of the incident."
She said the incident was "very unfortunate for all parties" and that she agrees with Quinones-Sanchez's calls for "a full investigation."
Quinones-Sanchez said police showed her video footage of the incident that made it clear that two people were involved.
"In one of those videos, [Diana] was clearly waving somebody down on Diamond Street," she said.
She said she doubted Diana's account that he alone had carried away TVs, a CD player, a stereo, jewelry, paintings, a suitcase and more while lighting the two fires investigators said had been set.
"His story and his version of the events are not plausible," she said.
Officer Leeloni Palmiero, a police spokeswoman, said investigators are not pursuing other suspects.
"The investigation is no longer ongoing," she said.
Neighbors approached by the Daily News yesterday said they would not discuss the incident because they feared retaliation.
Three who spoke on condition of anonymity said that Diana was living with a relative of Sen. Tartaglione's.
Diana's father, Billy Diana, owns El Sabor Restaurant, a block from both the Quinones-Sanchez house and the place where his son was living.
Reached by phone yesterday, Billy Diana said: "I don't want to get involved with this right now."
The councilwoman and her husband late last year moved out of the house that Diana allegedly broke into, and it was unoccupied at the time of the incident.
They since have moved into a house on the other side of Norris Square - reportedly to put them in the district of state Rep. J.P. Miranda. Tomas Sanchez reportedly considered challenging Miranda, who recently was charged in an unrelated ghost-employee scheme, before jumping into the Tartaglione race.
The councilwoman said yesterday that she still keeps things in her old place and visits it daily.
On Twitter: @SeanWalshDN