Prosecutors indicate that Ballout attempted to join the Islamic State in Syria during 2025 by traveling through Turkey to Lebanon. There, he encountered several individuals he believed were IS members.

Authorities arrested him in Lebanon in July 2025 and imposed a three-month prison term for inciting religious and sectarian strife.

He returned to Germany in November 2025, where officials detained him at Berlin Brandenburg Airport and held him in pre-trial custody.

In May this year, a Berlin court handed Ballout a juvenile sentence of one year and ten months for preparing a serious act of violence endangering the state.

The sentence was suspended as prosecutors appealed the verdict and sought a longer term.

Ballout was released under the supervision of a probation officer.

Interior Minister Alexander Dobrindt told RTL that the suspended sentence decision was certainly incomprehensible given the danger level in this case.

He added that authorities are investigating how the outcome occurred.

Berlin's Governing Mayor, Kai Wegner from the centre-right Christian Democrat party (CDU), expressed astonishment at how the Berlin judiciary handled Ballout's case.

He was sentenced under juvenile criminal law, Wegner told RBB TV. And then, unfortunately, the court imposed a suspended sentence. I do not want to judge that decision, as it reflects judicial independence, but I am truly at a loss for words.

The opposition far-right Alternative for Germany (AfD) party called the attack a complete failure of security policy.

If an Islamist threat known to police could carry out such an act, a thorough investigation must determine why he was still free to move about, said Martin Hess, the AfD's home affairs spokesperson.

According to Der Spiegel, Ballout told the Berlin court this spring that he had distanced himself from extremist ideology and violence.

Thomas Mücke, an extremism expert at the Violence Prevention Network VPN, told ARD television that he had met the suspect.

He said Ballout had given social workers a very composed, very cautious, very controlled and very friendly impression.

And those are precisely the criteria where we realise we cannot really get to know the person, he continued.

Some have called for Germany's laws against terrorism to be made stricter.

Peter Neumann at King's College London told ZDF that Germany's criminal law on terrorism is too lenient, and sentences too short by European standards.

He also called for a rethink of Germany's juvenile justice system, which he said prioritises education rather than public protection.

The home affairs spokesperson for the centre-left Social Democrats (SPD), Sebastian Fiedler, told Deutschlandfunk radio that criminal law was not the problem, but the way it was applied.

We need to look more closely at why Ballout was still at large. Another key question is what actually happened after his release from prison and who he remained in contact with. Although he was under surveillance, there was clearly a gap in the system.

Germany's Chancellor Friedrich Merz said it was too early to determine what political consequences will follow the attack, but promised action would be taken with prudence and determination.

He said if individuals classified as threats could not be detained, their freedom of movement should be restricted as much as possible.

I cannot understand how I can track my mobile phone from anywhere in the world, yet it is supposedly impossible or technically unfeasible for security authorities in Germany to determine the whereabouts of individuals classified as security threats to that same extent.

He said he had asked the interior ministry to review the law regarding monitoring jurisdiction.