The family of one of the victims in the Virginia Beach shooting on May 31 is asking that the city open an external investigation into the massacre, in which 12 people were killed.

Attorney Kevin Martingayle, representing Kate Nixon, a public utility engineer who was killed when the gunman opened fire at the Municipal Center, emailed a letter to city officials and council members Monday asking them to also release all the information and records about the gunman for further review, according to reports by the Virginian-Pilot.

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"This was an extraordinary tragedy. It was unprecedented," Martingayle told the local newspaper. "That calls for an extraordinary and unprecedented response."

The shooter, DeWayne Craddock, had worked for the city for 15 years as an engineer with the public utilities department. Prior to the shooting, he resigned his position "due to personal reasons," he wrote in an email he sent on the morning of the shooting.

Nixon, 42, who was married and had three daughters, called her husband around 4 p.m. on May 31 letting him know that she had been shot, Martingayle told the newspaper.

The family hopes that an external investigation, much like the one requested after the fatal 2017 protests in Charlottesville, Va., will bring clarity about what transpired that day and prevent future shootings from happening.

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City officials though believe "these requests appear premature while the criminal investigation is ongoing and these requests can be discussed and considered after, and with the benefit of, the findings of that investigation," they said in a statement.