Last week Berlin police reported that yet another woman had been attacked by an unknown man on a bicycle. It was the sixth such case since December, but unlike the five women before who were left injured in similar assaults, the most recent woman managed to block the attack with her scarf.

Police have been left scrambling for evidence to find the culprit or culprits, and they can’t even be sure that whoever is behind the attacks is the same person. But the modus operandi appears to be the same: A man on a bicycle rides up to a woman walking at night and sprays her with a liquid. The substance has been identified as battery acid in four of the cases, police told The Local.

“What happened at the crime scenes appears to be the same and we are investigating, but we cannot be 100 percent certain that it is the same person because we do not have him yet,” a police spokeswoman told The Local last week.

Given that the assaults all happened suddenly and in the dark of the night, the victims have only been able to provide a few details about their attacker’s appearance.

The latest woman who was left uninjured was able to give more of a description: that he was between 35 and 45 years old, light-skinned, of medium height and had a strong-looking build.

And the question remains of what would motivate someone to go after these seemingly unrelated women.

The director of Berlin Charité hospital’s Clinic for Psychiatry and Psychology, Isabella Heuser, has some ideas.

“I wouldn’t say that this is a random attack. The target seems to be young women out at night… If a man is doing this, it is probably a hate crime because for some reason he hates young women,” Heuser explained to The Local.

“The most likely reason that someone would commit these horrible crimes is that he might have have been rejected by a young woman.”

Heuser said that acid attacks are highly unusual in Germany, but that they happen more often in countries like India and Afghanistan when men decide they want to punish women or girls for what they think is inappropriate behaviour. In India, for example, lawmakers implemented harsher sentences for acid-throwing in 2013 due to the high number of incidents.

Heuser said the person behind the Berlin attacks displayed psychopathic features – not showing remorse or empathy towards the victims.

“A psychopath can on the surface be a nice guy, but they are all manipulative and they do evil things without any regard for feelings or the integrity of the victim,” she explained, adding that the Berlin cyclist “doesn’t talk or say anything, he does what he wants to do and then just rides away.”

But knowing that the culprit could be a psychopath who hates women does not add much to the ongoing police investigation. His choice of spraying acid at women rather than more physically attacking them also may be because he knows it will leave no DNA evidence behind, Heuser says.

“Unfortunately you are not going to be able to find him by profiling, which of course is a terrible thing to say because it means he can only be caught after he attacks again. There will have to be another woman who will be victimized, and that is horrible,” Heuser said.

One thing that could help narrow down the search is that the attacks all occurred fairly close to one another, mainly around the eastern districts of Prenzlauer Berg and Friedrichshain. This could mean that the culprit lives in that area – but Heuser said it could also be because the man knows women are often out walking at night in those areas due to the nightlife.

The victims themselves have no doubt suffered “deep psychological trauma” due to the attack, says Heuser. One of the women had to stay in hospital for a week due to injuries to her face, police said.

“This can be scarring for life, not only physically but also psychologically, but they have a good chance to overcome the psychological scarring,” especially if they undergo trauma therapy, Heuser noted.

The case has also had an impact on other people living in Berlin, which Heuser said is only natural.

“It’s simply scary to think ‘Oh God, I could have been there.’ Everyone walks around doing this and that without thinking about things, but even this now seems dangerous to them. This affects people’s sense of security, and people want to feel secure.

“Especially in Berlin where we have the luxury of being able to feel relatively secure, and then all of a sudden this happens… It’s really terrible.”