It's an odd topic, and I tend to spend hours each year reading over crime, murders and historical German events that fit within these areas.
So first, I tend to divide German mass murders into five groups.
The first group is the Roman-era, where you end up with mass murders (sometimes into the thousands).
The second group is the Catholic Church era. Some of these mass killings involve Jewish groups which became a target....some involve anti-church groups which weren't being cooperative with Church 'guidance'.
The third group comes after the Thirty Years War (ending in mid-1600s), and this mostly revolves around political revolt or rebellon.
The fourth group starts in the early 1900s, and you can say that the Bremen school shooting (by a nutcase school instructor) started the new era. In the Bremen case....the guy acquired several pistols at a local gunshop, and the gunsmith had reasons to suspect the guy was nuts. A local policeman was notified and even asked questions....but took the situation no further. On 20 June 1913....the nutcase shot five dead at the school and wounded around twenty others.
The fifth group starts up in the 1930s, with the Nazi apparatus chiefly responsible.
So as 1945 comes around....we revert back to the fourth group....private individuals.
Summer 1964, Koln, school attack....ten dead, twenty-two wounded. In this case, no pistol or rifle. The guy used a spear and flame-thrower.
October 1980, Oktoberfest bombing. 13 people dead, over 200 wounded. The police would eventually figure out the bomber (he was among the dead) as being an emotionally fragile person, somewhat connected to Nazi groups, having failed his occupational exam, and a loser at relationships. While some of this was true....no one wanted to talk about the potential for accomplishes. In the past five years....ample evidence has come out to say at least one other individual was involved in the planning for this.
Summer 1983, Eppstein school (across the valley from my village). This was a mid-30s Czech refugee who was considered 'gifted' but also never achieving much in life. In this school shooting, six dead and fourteen wounded.
Spring 1993 Solingen fire attack. No weapons used in this attack. Four skinheads set fire to a house that Turks lived in. Five dead, fourteen wounded. It set off a full year of hostilities by the Turkish community in NRW. For the skinhead 'community', it invited in massive government surveillance, and downsized them.
Spring 2002 Erfurt school shooting. The guy involved (age 19) was considered 'gifted' but also had various personal problems which could never be detailed or explained. At some point, he skips four days of school (even to this day, no one can say what he was doing). Asked for a medical slip....he forged it, and got caught....then was expelled from the school. Shortly after that, he shot his way through the school (killing 17).
Summer 2007 Duisburg 'massacre'. This is one of those stories that ought to be made into a movie. What you had was a group of six Italians killed in their cars in front of a pizzeria shop. One of the guys had already murdered another mob-related guy, and this was a retribution episode. The suggestion that this opened up a Italian mob 'war' in Germany? It gets openly discussed but never goes far.
Spring 2009 Winnenden school shooting. Sixteen dead, nine wounded. The shooter? Young kid, 17 years old. This was a kid who marginally got through school, and upon completion....when you'd go and enter an apprenticeship.....no one wanted to 'hire-up' the kid. So he went into an emotional tailspin....going back to the school to shoot it up.
Summer 2016 Munich shooting. This centered around a shopping mall, with ten dead and thirty people wounded. Shooter? This 18-year old was an Iranian-German (parents had come years before). Digging through everything....the kid was bullied most all of his years in school. As many positive things as they found....the kid never got ahead of the emotional burdens, and this attack was simply revenge for the bullying. Weapon used? Off Dark-Net.
Fall 2019 Halle shooting. Two dead. This was an attack aimed at a Jewish synagogue. Based on various accounts, this 'kid' had consumed an awful lot of propaganda and had reached some frenzied state of mind where he felt the attack was justified. Captured alive, he was set for life in a holding facility, but for a brief five-minute period in 2020....he escaped. I should note here....the weapon used? Home-made....not purchased.
As much as shootings get front-page news in the US and linger around for years as a anti-gun topic.....German stories like this get front-page coverage for about ten days.....then get some update six to twelve months later after the investigation/court case concludes.....then is dropped from history for the most part.
Some are nutcases.....some are people with political agendas (left and right)....some are religious-fever type individuals (radicalized)....some relate to bullying...some suffering from a mental breakdown (that Bremen episode is a classic example of that). Some are German....some are 2nd generation German. Some are resident guests.
The only odd characteristic you can draw from all of these.....none were conducted by women.
But I'll add this one observation here at the end....if you use all of the past two thousand years of Germany (particularly the Roman era)....a whole lot of killing has taken place, and anyone claiming a 'final' chapter....only has to wait a year or so....for another chapter to be written.