The Boston police bomb squad investigated a pressure cooker found on Lexington Street in East Boston on Tuesday morning, but determined it did not contain explosives, police said. The investigation led staff at the nearby Hugh Roe O’Donnell Elementary school to put the school into “safe mode,’’ said Boston public schools spokesman Brian Ballou. The school backs up to the property that police were investigating. Police believe the pressure cooker had been discarded, a spokesman said. Bombs made from pressure cookers were allegedly used in the April 15 Boston Marathon bombings. (Globe Staff and AP)Material from The Associated Press was used in this report. John R. Ellement can be reached at email@example.com. Follow him on Twitter @JREbosglobe.