San Jose residents remain on edge as authorities search for the serial arsonist accused of setting roughly a dozen fires in under a week.

Authorities ruled out arson as the cause of a two-alarm blaze near Alum Rock Park Monday, saying it was not connected to the 13 fires set in and around the downtown area of the city in the last week. But the early morning fire, believed to be caused by a smoker outside on a deck on the 17000 block of Crothers Drive, ignited fresh fears about the serial fire-setter’s work.

"Everybody's just scared right now," San Jose resident Jose Lara said. "Everybody's just thinking about it. To see where he's going to target. Where he's going to do his thing and stuff. Everybody's afraid."

Investigators said the arsonist is starting fires on people's porches and torching things like newspapers and furniture. Resident Betsy Long said she purchased a motion-detection light for her porch as well as a chain to lock her front gates in response to the fires.

"You're so vulnerable," she said. "Basically I feel like I should sit out here all night long and sleep during the day."

There were five arsons reported over the weekend, including three on Sunday. Two of those three fires were reported on South 24th Street and in the lot of the Greater Saint John Baptist Church at 1230 E. San Antonio St., which had been damaged by another arson fire on Wednesday.

MORE: $10,000 Reward for Arsonist

Police said that these small blazes are likely connected to fires set on Wednesday, Thursday and Friday, all between the hours of 2 a.m. and 6 a.m. They were all reported between Santa Clara and William streets.

"We have experienced a rash of very dangerous fires that our fire officials will inform you have been intentionally set," San Jose Battalion Chief Robert Sapien said. "These fires have targeted San Jose residents in the darkest hours of the night when they are most vulnerable. We have been very fortunate that these incidents have not resulted in serious injury or death to our residents. Should these fires continue, I feel that this good fortune could run out."

MORE: San Jose Arson Team Investigates 4 "Intentionally Set" Fires

On Saturday, the San Jose Firefighters Association put up a $10,000 reward for information leading to the arrest and conviction of the person, or persons, responsible for starting these fires. Investigators released a sketch of the suspect -- a "real skinny" man with distinctive large frame glasses -- based on witness descriptions and images taken from surveillance cameras.

The suspect is described as about 25 to 40 years old and 6 feet to 6 feet 2 inches tall, weighing between 160 and 180 pounds.

His hair is dark and medium-length, and he wears distinctive large frame glasses.

Dr. Leonard Donk of Cupertino, a forensic psychologist and criminal profiler who has analyzed the work of previous serial arsonists, said the man behind the latest blazes is likely "not a pro" since he does not appear to use gels or accelerants.



Donk said the arsonist in this case is probably from the same neighborhood and has few friends.



“First of all, he’s an angry guy,” Donk said. “Very much into destruction. Doesn’t know what it’s about. Could be vandalism, could be attention seeking.”

NBC Bay Area's Peggy Bunker, Kim Tere, Damian Trujillo and Bay City News contributed to this report.