Report: Email threat said "Time for more police to die"

PORTLAND, Me. -- Police in Portland, Maine are investigating "pointed" threats referencing killing Portland police officers with assault rifles, police chief Michael Sauschuck said.

The Portland Press-Herald reports at least two staffers at the newspaper received an an email threat around 8:45 a.m. Wednesday that read, in part, "time for more police to die."

The email said the writer and his or her "partners" were "getting our Sig Sauer MCX .223-caliber rifles ready" and intended to "shoot and kill as many police officers as they can," the paper reports. The writer also said they planned to "get into position" on top of the Cumberland County Parking Garage, nearby the city's police headquarters, and that they had booby-trapped the garage with explosives.

The paper shared the email with police.

Speaking at a brief press conference, Sauschuck didn't give any indication as to whether investigators believe the threats are credible. But he said they were "direct and very pointed, and did involve the use of assault weapons and killing police officers and specifically killing Portland police officers."

Sauschuck said the department on Wednesday morning used bomb-detecting canines to search the garage referenced in the threat and didn't find any indication of explosives. The garage - which reportedly serves as both public parking for the Cumberland County Court and parking for police cruisers -- was expected to remain closed as the investigation continued.

The police department, Sauschuck said, remains "open for business."

The department also received similar apparent threats over Twitter Wednesday, the paper reported.

"The tweets are relatively new to us," Sauschuck said. "We've been working with the email all morning. We'll see if there's any connection."

The threats come at a time when police departments across the nation are increasing officer safety measures in the wake of fatal police ambushes in Dallas and Baton Rouge. Experts tell CBS News both online threats to police and surprise attacks on cops are on the rise.

"We've told our officers to be safe - we've been sending that message for the last few months," Sauschuck said. "We're making arrangements to make sure they're safe."