Jewish community leaders in Germany have criticised the police’s “scandalously” slow response to the terror attack on a synagogue in eastern Germany.

A gunman in military outfit went on a rampage in the city of Halle, killing two people, with further bloodshed averted only because the attacker’s homemade firearms malfunctioned.

The president of the Central Council of Jews in Germany said the police had been slow to come to the rescue of 60-70 people inside the synagogue in the city’s Paulus quarter, after the attacker tried to shoot open the gates.

“It’s scandalous that a synagogue in Halle isn’t being protected by police on a holy day like Yom Kippur,” said Josef Schuster.

In response to the attack, Germany’s interior minister announced his ministry would permanently improve security measures at synagogues across the country. “This government will do everything to make sure that Jews can live in this country without threats, without fear,” said Horst Seehofer.

Footage broadcast on a livestreaming platform suggests the deadly attack would have ended with many more victims if the gunman’s homemade firearms had not malfunctioned.

The suspect, named by media as a 27-year-old German citizen, Stephan Balliet, broadcast his rampage on the Twitch platform.

The footage shows the suspect becoming increasingly frustrated as his homemade weapons repeatedly malfunction. In at least three instances the video shows the suspect pointing a gun directly at a victim only for the weapon to jam.

A screenshot of a video shows the gunman firing a weapon. Photograph: Andreas Splett/EPA

Calling himself a “loser”, at one point he says: “I have certainly managed to prove how absurd improvised weapons are.”

Germany’s chief federal prosecutor, Peter Frank, said on Thursday that the suspect wanted to carry out a “massacre” and had about 4kg of explosives in his car.

Balliet, who lived with his mother in the municipality of Helbra, about 40km from the site of the attack, has been described in German media reports as a loner with few close friends, who spent a lot of time in front of his computer.

A mission statement that was first uploaded on the obscure meguca.org imageboard and then reposted on a number of forums, where it was later found by researchers at the International Centre for the Study of Radicalisation at King’s College, London, appears to confirm the use of homemade firearms built according to plans released by a British pro-gun activist from West Yorkshire.

Philip Luty, who believed British gun control laws were “fascist”, devoted his life to publicising blueprints for making firearms from easy to obtain materials, with the goal of allowing private citizens around the world to flout gun restrictions by building weapons at home.

When he died of cancer in 2011, Luty, 46, was facing three terrorism charges for manuals he had published explaining how to build firearms, including a 9mm submachine gun, according to the Yorkshire Evening Post.

The Halle suspect appears to have used one of these homemade Luty submachine guns, as well as other homemade guns and hand grenades, according to the Kohlchan documents.

The documents suggest he used homemade guns intentionally, with the goal of “showing the viability of improvised guns” for people who want to carry out terror attacks but who do not have access to commercially made weapons.

The footage of the shooting suggests the homemade guns malfunctioned, which may have helped prevent more murders. After attacks on both a synagogue and a kebab shop, according to the livestreamed footage, the gunman said: “Sorry, guys, the fucking Luty is shit!”

Both the documents and the livestreamed footage suggest the gunman was a white nationalist, and that he hoped his attack would inspire other white people to kill more Jewish people, as well as other people he perceived as enemies of the white race, including Muslim people, black people, anti-fascists, and communists.

The mission statement also shows that he deliberately chose to carry out his rampage on Yom Kippur but was wary of the synagogue being heavily secured, and considered attacking a mosque or an “antifa culture centre”.

Germany has strict gun laws and rigorous procedures for buying weapons, but it also has very high rates of private gun ownership.

While German authorities have not yet confirmed the types of weapons used in the attack, some arms experts online said it was clear from images of the weapons used in the attack that at least one of the guns was built from a distinctive Luty submachine blueprint.

Luty, described as a “loner” who lived with his parents, was sentenced to four years in prison in 1998 for building a prohibited weapon, a submachine gun, and for illegal possession of ammunition, the Sunday Telegraph reported.

But he continued what he called his “no compromise stance on gun rights issues”, and went on to publish multiple books with an American publisher describing how to make homemade guns.

In 2009, firearms officers arrested Luty and searched his home. He faced new terrorism charges related to “making a record of information likely to be useful to a person committing or preparing an act of terrorism”, according to a spokesperson for the counter-terrorism policing unit in West Yorkshire. He died before the case went to trial.

The German president, Frank-Walter Steinmeier, (second right) and his wife, Elke Buedenbender, speak with Rabbi Elisha Portnoy in Halle on Thursday. Photograph: Henning Schacht/German federal government/EPA

The Metropolitan police declined to comment on Wednesday evening.

The Twitch video, seen by the Guardian, suggests that the attacker was on the street outside the synagogue for more than five minutes, during which time he shot and killed a passerby, without being approached by law enforcement.

After a visit to the synagogue on Thursday, President Frank-Walter Steinmeier said Germans needed to united against extremism.

“Today is a day of shame and disgrace,” Steinmeier said. “I’m very sure the overwhelming majority of this society in Germany wants Jewish life to be part of this country … We must stand together long term against violence like we experienced here yesterday. We must protect Jewish life.”

• This article was amended on 14 October 2019. Based on information from the International Centre for the Study of Radicalisation (ICSR), an earlier version said that the suspect uploaded a mission statement to the German message board Kohlchan. After publication, the ICSR said that in fact the manifesto was originally posted on the meguca.org imageboard. This has been updated.