Police in Randolph are investigating after an empty shell casing was found in an elementary school classroom Tuesday morning, the third shell casing discovered in that classroom this month, according to police.
The shell casing was found in a fourth grade classroom at Donovan Elementary School at around 9:30 a.m., said Leah Comins, a police spokesperson, in a phone interview Tuesday.
Police responded, took custody of the casing, and searched the classroom, Comins said.
The school initiated a shelter in place for about 40 minutes, police said.
Two other shell casings were found on Jan. 13 and Jan. 19 in the same classroom, the Globe previously reported. All of the shell casings were empty and did not contain live rounds.
Police believe all three shell casings are related.
The Randolph Public School superintendent was not immediately available for comment.
The incident remains under investigation by Randolph police.
Material from prior Globe stories was used in this report.
Matt Yan can be reached at matt.yan@globe.com. Follow him @matt_yan12.