PORT RICHMOND, N.Y. -- Investigators initially thought a 14-year-old slashed his siblings' throats and set his house on fire, killing the family of five. But they are now shifting the focus of the case and believe the late mother may be responsible for the fatal tragedy on Staten Island.

Cops originally thought C.J. Romoy, 14, killed his siblings, torched the house and committed suicide.

He was found with a razor blade underneath his body and had a history of behavioral problems and setting fires.

But autopsy reports state that C.J. Romoy and his sisters -- 10-year-old Brittney and 7-year-old Melonie -- were already dead before the fire was set and did not die from smoke inhalation.

All three kids were found with their throats slashed.

Reports say Leisha Jones, 32, wrote the badly charred signed note with the words "am sorry," which was found in the house on Nicholas Avenue in Port Richmond.

They believe she may be the one who committed the murder-suicide and arson that killed herself and her four children on Thursday.

"We believe both the note and the diary were written by the mother," NYPD spokesperson Paul J. Browne stated in an e-mail.

Jones and her 2-year-old Jermaine Sinclair died of smoke inhalation, according to autopsy reports.

Young Jermaine Sinclair, who was found near the front door, was rescued from the blaze but died at Richmond University Medical Center in West Brighton.

The autopsy report also showed that Jones and her 14-year-old son had undigested pills in their stomachs, suggesting she may have tried to commit suicide or she may have needed to drug her son before killing him.

The New York Post reported Monday that, months ago, Jones told a female friend she had contemplated killing her children and setting her 2 1/2-story house ablaze.

According to the Post, C.J. Romoy's father Earlston Raymond, who lives in Jamaica, said Jones told their mutual friend: "At times, I feel like killing the kids and burning the house down and killing myself."

He alleges he did not learn of this threat until after Thursday's tragedy.

Neighbors steadfastly dismissed the allegations against the 14-year-old and described him as being "the most loving person in the world" who helped care for his younger siblings.

After being evicted from her Washington, D.C. apartment, Jones moved her family to Port Richmond.

But she had difficulty paying her rent and, in 2007, was sued by her landlord for $7,000 in back rent.

Jones was a single mother with children sired by different fathers.

She was working part-time as a security guard in the Macy's at Staten Island Mall to make ends meet.