A handgun was found at a Catholic high school during school hours on Monday, police said. The weapon was located by a school employee at Union Catholic High School in Scotch Plains about 10:45 a.m., the Scotch Plains Police Department said in a news release. The school was placed on lockdown until 2:40 p.m. while police investigated the incident. A shelter-in-place was also conducted at Scotch Plains-Fanwood Public Schools as well as the public school district in the neighboring town of Westfield. There were no indications of threats or harm to the school and the building is now considered saf…