The unborn baby of a woman who was seven months pregnant was among those killed during a mass shooting at a Jehovah’s Witness building in the German city of Hamburg.

Police identified the gunman as Philipp F, a 35-year-old German with no prior offences who had been a member of the congregation – but had left 18 months ago with “ill feelings”.

Police said they had received conflicting reports as to whether he was excluded or left of his own accord.

They also revealed an anonymous letter had been sent to officers in January saying the attacker should not be allowed to have weapons and that he might be suffering from a mental illness.

The letter also said he was “enraged” with Jehovah’s Witnesses and a former employer.

Two police officers visited the gunman’s apartment unannounced in February after receiving the anonymous letter to perform a check but found he was “cooperative” and they did not remove his weapon.

Six people and an unborn baby died in the incident, as well as the attacker who took his own life.

Officials also said:

• Among the dead were four men and two women and the unborn baby. Police confirmed the attacker was not related to any of those killed. All were German citizens

• The mother of the unborn child survived the shooting

• Eight people were wounded, four of them seriously. Six of the eight injured are German, one is Ugandan and one is Ukrainian

• There were 50 people in the congregation at the time of the shooting. Twenty were able to flee from the building unharmed when the gunman entered

At a news conference, Hamburg’s interior minister Andy Grote said the lone gunman was isolated by police when he ran to the floor above where the shooting took place and took his own life.

The gunman fired more than 100 rounds during the shooting.

Police also said that before the attacker went into the building, he fired 10 shots at a woman in a car parked outside – but she managed to get away and notify police.

Mr Grote called it a “horrific crime” and “very cruel”.

He said it was “something we’ve not experienced in the past – we see it on TV, we see it elsewhere, we’ve never seen it happen in our city”.

“It was the worst crime that our city has experienced recently,” he added.

Police were alerted at 9.04pm local time on Thursday to the attack at the Jehovah’s Witnesses’ Kingdom Hall in the Gross Borstel district of Germany‘s second largest city. Police received a total of 47 emergency calls about the incident.

A special operations unit of the police that was nearby arrived at the site at 9.09pm, with officials saying it was likely the unit’s fast arrival saved lives.

Hamburg police chief Ralf Martin Meyer said the man had a weapons licence and legally owned a semi-automatic pistol.

Officials also confirmed the gunman was unmarried and working in Hamburg.

Apart from the anonymous letter, police said no other reports were made against Philipp F previously and he had not committed any offences.

But officials said the gunman had reported a potential fraud to police, which is now being investigated by prosecutors.

Police also confirmed they searched the gunman’s apartment at 12.30am on Friday morning, more than three hours after the shooting, and found another 15 loaded magazines and four packs of ammunition. Police also seized laptops and smartphones from the apartment.

In line with Germany’s privacy rules, police can not release the gunman’s full surname.

German Chancellor Olaf Scholz, a former Hamburg mayor, described the shooting as “a brutal act of violence” and said he was “speechless”.

Mr Scholz also said authorities “fear further victims may die from their severe wounds”.