WESTPORT — Police have stepped up presence at the town’s schools Tuesday after a violent threat was found scrawled in a Staples High School bathroom Monday, and another apparently unrelated threat was posted on social media by a local juvenile later in the day.

Threatening messages on social media, which “caused concern and alarm to those who viewed them,” prompted a police investigation Monday evening, Lt. Eric Woods, the police spokesman, confirmed Tuesday.

The person responsible was identified, Woods said, and “he was charged accordingly.”

That incident is believed to be unrelated to threatening graffiti found at Staples earlier in the day, Woods said.

That graffiti was discovered in a girls’ bathroom at the high school, and according to an online report by Inklings, the Staples newspaper, read:

“smart school boy 9 gonna get ya!! I’m going to shoot the school up this tuesday …”

After the graffiti was investigated by school officials and police, it was judged “non-credible in nature,” according to an email Principal Stafford Thomas sent to the Staples community Monday afternoon.

The principal added: “I would like to commend our students who saw something and said something as this is an effective way to alert our security and administrative teams to conduct more precise investigations.”

Supt. of Schools Thomas Scarice, in a message emailed to the entire school district, elaborated on the Staples incident, writing: “… The administration was made aware of language found on a wall in a bathroom stall which would be considered threatening to the school.

“The team spent the day working with the Westport Police Department, up to the level of the chief of police. This threat was not deemed credible, yet, in an effort to reassure the school community, the decision was made to have multiple Westport police officers stationed on campus,” he said.

And, in reference to the social-media threats, the superintendent added: “Additionally, I can assure the school community that the individual who was identified as the source of the social-media posting will not be in school [Tuesday].”

The school graffiti remains the subject of an open police investigation, Woods said Tuesday.

In response, he added, there is increased police presence at the schools Tuesday “to try an alleviate any fears students/staff may have with going to the schools.”