PLYMOUTH — Classes began and ended without incident at Plymouth High School Friday, after a bomb threat was found earlier in the week.

James Condon, PHS principal, said attendance Friday, which was optional with parental permission, was "very low."

David Bacon, assistant Plymouth police chief, was inside the school when classes began on time Friday morning. Bacon said a police canine had assisted with a search of the school Thursday night.

"Nothing suspicious" was found, Bacon said.

Other police officers patrolled the parking lot during the early hours. Only the front lot, where staff members park, was full Friday.

Andy Langdon, a sophomore, and his buddy, Andy Sanchez, a junior, weren’t letting the bomb threat keep them away from important classes.

Both said they had chemistry to attend to, and neither was concerned about the threat.

"My mom was a little nervous," Langdon admitted. "But my dad said, ‘Go for it!’"

Sanchez said his parents had told him that the high school was "probably the safest place in Plymouth to be today" because of the police presence and steps officials had taken to ensure student safety.

Both Condon and Bacon said authorities had made progress in trying to find out who was behind the bomb threat. Condon said he announced Friday morning that he would reward any student who helped with the identification of the person who made the threat.

"I don’t know what it (the reward) will be," Condon said, "but it will be good."

Bacon said parents, students and the school community had been offering information to both his officers and school officials. He had hopes this morning that a possible suspect would be questioned yet that day.

The threat was found Tuesday in a message written on a bathroom stall in the high school. It warned that a bomb would be detonated at noon Friday at the school.

Officials contacted police, met with faculty on Wednesday, and on Thursday told the entire student body over the public address system of the threat. Letters from Condon were sent home Thursday afternoon with students to parents and guardians.

Students were restricted to entering the school through certain doors Friday morning, and were told not to take large carry-alls or backpacks in with them. Condon also prohibited students from entering the school before 7:15 a.m.

The principal had said Thursday that attendance Friday would be "optional" and students would not be penalized if they had parental permission slips to be absent.