Suspected Capital Gazette shooter Jarrod Ramos legally purchased pump-action shotgun within last 18 months

Jarrod Ramos legally bought his pump-action shotgun within the last 18 months, police said, despite a years-long history of threatening behavior, including against the Annapolis newspaper at the center of a deadly shooting Thursday afternoon.

Ramos allegedly stormed the Capital Gazette newsroom just before 3 p.m. and opened fire, killing five people and injuring several more. The 38-year-old, from Laurel, Maryland, was arrested and charged with a count of first-degree murder for each victim.

“We’re frustrated I think,” Anne Arundel County Police Chief Timothy Altomare told CBS Friday morning. “We know what happened. We’re still working on a lot of the whys.”

Investigators have done everything they “physically” need to do at the crime scene and have executed search warrants at the suspect’s home. They did find “some evidence that shows origins of a plan” and “continuation of thought,” Altomare said, but they did not “find any real motivator.

Ramos did appear to harbor a deep resentment for the paper, which featured a 2011 story that covered a criminal harassment charge against him. In July 2012, Ramos filed a defamation lawsuit against former columnist Eric Hartley and then-editor Thomas Marquardt, which was later dismissed.

“I for one received what I considered to be a death threat,” Marquardt told CBS News. “I feared for my life, I feared for my family’s life and I feared for my staff’s life.”

More on the Capital Gazette shooting:

The former Gazette editor said he went to police at the time, but was told nothing could be done. Altomare said newspaper management and law enforcement came to a “shared conclusion that carrying action further may exacerbate the situation."

A Twitter account believed to be Ramos’ — which boasted an avatar with Hartley’s photo Thursday — regularly commented on the Anne Arundel County news and often referenced the 2015 shooting at the French newspaper, Charlie Hebdo,

That account had been dormant since January 2016, but just minutes before the shooting, a new tweet was posted: “F--- you, leave me alone.”