German prosecutors said Thursday they are investigating an official at Hamburg's firearms department and three members of a gun club in connection with a mass shooting during a religious service at a Jehovah's Witness hall last month.

A 35-year-old German man opened fire during the March 9 service, killing six people and wounding nine, including a pregnant woman who lost her unborn child, before turning the gun on himself as police arrived.

Hamburg prosecutors said authorities searched the homes of an official at the city's firearms department and of three members of the Hanseatic Gun Club that the attacker — identified only as Phillipp F. due to German privacy rules — had been part of.

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Prosecutors said the firearms official is being investigated on suspicion of negligent homicide for failing to properly document and forward information about the gunman's psychological state that he had received from F's family, via a member of the gun club.

Because the official had registered the tip as being "anonymous," despite knowing its true source, authorities only ordered an unannounced visit to F.'s home rather than seeking further information.

Prosecutors are investigating three members of the Hanseatic Gun Club's board of examiners on suspicion of issuing a certificate dated April 28 falsely stating that F. had passed an exam on firearms knowledge, even though he had failed and had to retake the test later in the year. Had authorities known of this, they might not have issued F. with a license to own firearms in December, prosecutors said.

F. was a former member of the Jehovah's Witnesses who left voluntarily about two years ago, the church says.