The man who pleaded guilty to firing an assault weapon in a Washington, D.C., pizza shop to investigate an internet conspiracy theory has been sentenced to four years in prison.

Prosecutors argued that a tough sentence would "deter other would-be vigilantes," and initially aimed for a four-and-a-half-year prison term of Edgar Maddison Welch.

Welch, from North Carolina, walked into the Comet Ping Pong restaurant in northwestern Washington in December and fired a weapon.

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He told police that he was investigating a conspiracy theory holding that the restaurant was being used by former Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonBloomberg rolls out M ad buy to boost Biden in Florida Hillicon Valley: Productivity, fatigue, cybersecurity emerge as top concerns amid pandemic | Facebook critics launch alternative oversight board | Google to temporarily bar election ads after polls close Trump pledges to make Juneteenth a federal holiday, designate KKK a terrorist group in pitch to Black voters MORE and her campaign chairman to operate a child sex trafficking ring.

Welch, who had with him an AR-15 rifle and a 0.38 revolver when he entered the restaurant, "surrendered peacefully when he found no evidence that underage children were being harbored in the restaurant," according to court documents.

Welch pleaded guilty in March.

In an apology letter, Welch said that he "came to D.C. with the intent of helping people" and that he never intended to do any harm.

"It was never my intention to harm or frighten innocent lives, but I realize now just how foolish and reckless my decision was," he wrote in a letter included in a sentencing memorandum.