MINNEAPOLIS (AP) -- The suspect in the fatal shooting at a Minnesota medical clinic was able to enter the building despite threatening violence there two years earlier.

Documents show Gregory Paul Ulrich also once posted a sign near his home about a doctor at the clinic he disliked and frightened a nurse at a nearby hospital so much that a colleague hit a panic button for help.

Despite these red flags, authorities say the 67-year-old entered an Allina medical clinic northwest of Minneapolis on Tuesday and opened fire, killing one staff member and injuring four others before he was arrested.

One security expert says it’s not clear whether police could have done more to prevent the attack.

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