(CNN) -- A 17-year-old boy appeared in a California juvenile court on Tuesday in connection with a small fire that occurred during several wildfires last week in San Diego County, authorities said.
No further details were available on the nature of the juvenile court appearance for the teen, said spokeswoman Tanya Sierra of the San Diego County District Attorney's Office. The juvenile court judge closed Tuesday's proceedings to the media, and authorities weren't releasing details because of the individual's juvenile status, Sierra said.
The 17-year-old boy was arrested last week with a 19-year-old man, but the older teenager was released and there will be no charges filed against him, Sierra said Tuesday. Both individuals are from Escondido in San Diego County, and the small fire that prompted their arrest Thursday was extinguished, authorities said.
"We can only file charges when we believe we can prove them beyond a reasonable doubt, and in this case, after a thorough review of the case, the district attorney's office declined to file criminal charges" against the 19-year-old man, Sierra said.
Authorities have already charged Alberto Serrato with arson in connection with another small fire last week. He is accused of adding brush onto an existing small fire in the San Luis Rey riverbed area in Oceanside, authorities said.
Serrato, 57, pleaded not guilty on Friday, Sierra said. Serrato is the only person charged with arson in last week's wildfires, which at one point numbered about three dozen.
In all, nearly 26,000 acres, or about 40 square miles, were burned the past week by nine major fires in San Diego County, Cal Fire spokesman Daniel Berlant said Tuesday.
On Tuesday, all but three wildfires were completely contained.
The Cocos Fire in San Marco burned 1,995 acres and was 93% contained Tuesday, Cal Fire said.
The Pulgas Fire on the Marine Corps base Camp Pendleton burned 14,416 acres and was 99% contained Tuesday afternoon, Cal Fire said.
The San Mateo, or Combat Fire, also on Camp Pendleton, burned 1,457 acres and was 99% contained Tuesday afternoon, Cal Fire said.
The two fires and others on Camp Pendleton last week burned 21,900 acres, almost 18% of the base, the Marines said.
San Diego County authorities have formed a task force to investigate more than a dozen wildfires from last week, said Jan Caldwell, spokeswoman for the San Diego County Sheriff's Department.
"The purpose of the task force is to be a clearinghouse for investigators to look for similarities in these cases," Caldwell said. "They will do trend analysis and look for patterns."
A second task force with the district attorney's office and state insurance authorities was also warning homeowners on Tuesday to be wary of criminals who prey on victims of natural disasters, the district attorney's office said.