1. Two people are still fighting for their lives
The teenager boarded the train at Ochsenfurt station, just south of Würzburg in Bavaria, and attacked passengers with an axe and a knife at some point shortly before 9.15 pm when the emergency brake was pulled.
He then fled the train and attacked a woman walking her dog along the river. Shortly after he was shot dead by a special operations police unit who happened to be in the area.
Luckily, by Tuesday evening, no one had yet died in the incident other than the attacker himself.
However the police chief in Würzburg Gerhardt Kallert said on Tuesday afternoon that two of the victims were still in a life-threatening situation.
Three of the four victims were members of one family from Hong Kong. The fourth victim was a family friend of theirs.
The injuries are “very bad and very drastic,” Kallert said.
2. Isis have taken responsibility for the attack
On Tuesday morning the terror-group Isis claimed that the Afghan teenager was one of “their soldiers.” It is the first time they have claimed an attack in Germany.
A statement released through the group's news agency claimed he had "executed the operation in response to calls to target nations in the coalition fighting the Islamic state."
Later in the day Isis published a video on the internet which appears to show the attacker.
The video shows teenager "Mohammed Riyadh" - knife in hand - announcing in Pashto he would carry out an "operation" in Germany, and presenting himself as a "soldier of the caliphate".
3. Investigators believe attacker radicalized himself
Bavarian interior minister Joachim Herrmann said on Tuesday that investigators believe the teenager, who arrived in Germany in 2015, had radicalised himself in recent weeks.
In his room they found a homemade Isis flag and texts in Arabic and Latin scripts which suggested he had become radicalized while at home.
Investigators said on Tuesday that he did not regularly attend mosque, but prayed often by himself at home. They also said that while he was active on social media they have not found any evidence of Islamist leanings in what he wrote online.
4. A religious motive is pretty certain
Several eye witnesses have now said that they heard the teen screaming 'Allahu Akbar.' There also appears to be a recording of an emergency call with him shouting these words in the background.
Furthermore, police found a letter in the boy's bedroom which they believe was a farewell note to his father. In it he wrote “pray for me that I seek revenge on the unbelievers and pray for me that I go to heaven.”
5. Death of a friend in Afghanistan could be key
Prosecutors revealed on Tuesday that a friend of the attacker died in Afghanistan on Friday or Saturday. This led to him contacting people back home repeatedly over the next two days.
His mobile phone was only located on Tuesday afternoon, as it had fallen onto the ground between the train and the nearby river bank. But prosecutors hope it will provide more clues.
While prosecutors are cautious to say what the significance of this event could be, it seems possible that it served as a catalyst for his brutal rampage.
6. Police ‘right' to shoot attacker
A Green politician caused a storm by suggesting that police could have shot the attacker to disable rather than kill him.
Many social media users were outraged by the apparent questioning of the moral integrity of officers only hours after they had put an end to a highly dangerous situation.
Prosecutors supported the special police forces at a press conference on Tuesday.
They described how the young Afghan had attacked the cops “as if he were in a trance” and that this had justified the use of deadly force.
One Würzburg prosecutor said he was “completely convinced the police were justified in shooting the attacker dead.”
He said he could "in no way understand how politicians sitting in their chairs can make such comments."
7. ‘Isis will seek to exploit attack'
An expert on Isis told The Local that the terror group will seek to exploit the attack for their own advantage.
Isis will use the attack to split German society, Dr. David Arn of Ludwig Maximilian University predicted, adding that this is part of a strategy developed in 2015 called “extinguishing the grey zone".
“By this they mean eradicating the ‘grey area' in which Muslim can live in 'the land of the unbelievers.'
"They want to create a situation where the security measures against refugees become so restrictive that it becomes impossible for them to live in Europe anymore, or alternatively that an Islamic state is created in Europe as well.”