Several people have appeared at a court hearing into the bloody shooting at their high school in the northern US state of Minnesota last month.
More than two-thirds of Red Lake's pupils stayed away on Tuesday
A grand jury is looking into the massacre, in which a pupil shot dead nine people before killing himself.
Another schoolboy has been arrested over the attacks, and federal officials are said to be investigating whether others were linked to it.
The hearing began on Wednesday, a day after classes resumed at the school.
More than two-thirds of pupils stayed away, with many fearing a repeat of the massacre, though attendance improved slightly on Wednesday.
Community leaders in Red Lake, a Native American reservation, say uncertainty about the court case is fuelling anxiety in a local population already on edge.
'Somebody to blame'
At least 12 adults and four teenagers were seen entering the courthouse in the city of Minneapolis on Wednesday, the Associated Press news agency reported.
Weise's massacre was the worst since Columbine
Most refused to talk to journalists, or were shielded by federal marshals. No details of the proceedings were released.
One Red Lake resident, who identified herself as Val Desjarlait, said her brother had testified.
"All of us are questioning why we have to be here," she said, quoted by the Star Tribune newspaper.
"I think they just need somebody to blame."
Daniel Gerdts, a lawyer for one of the juveniles called on to testify, said he had filed an order to quash the summons.
The authorities had not said why they wanted to talk to his client, he added.
AP said investigators were looking at a small number of potential co-conspirators and a larger number of pupils who may have had some prior knowledge of the attack.
Gunman Jeffrey Weise, 16, first killed his grandfather and his grandfather's partner at their home before heading to the school.
There he killed a teacher, a security guard and five students - the youngest 14 - during a 10-minute rampage.
It was the deadliest school shooting since the Columbine killings in 1999 when two teenage gunmen killed 13.
Another 16-year-old, Louis Jourdain, was arrested a week later on charges of conspiracy to commit murder.
His father, Red Lake tribal leader Floyd Jourdain, says he is innocent.