After the acid attack on top manager Bernhard Günther in Haan near Düsseldorf, one of the perpetrators is said to have given himself away.
A lawyer testified on Tuesday at the Wuppertal district court.
He recounted his meetings with an anonymous tipster.
He had gotten the already suspended investigations rolling again and received a reward for it.
Wuppertal - He first named a martial artist who is said to have been involved in the attack and then, in return for a further payment, gave information about the current defendant.
When asked how he got the explosive information, the tipster said: "One of them gave it away."
The man said he was afraid for his life and therefore did not want to speak to the police, the 48-year-old lawyer said.
He had met him several times in different hotels.
The whistleblower gradually gained confidence.
Günther, now 55, was attacked and burned near his home in Haan near Wuppertal on March 4, 2018.
The perpetrators had poured highly concentrated sulfuric acid over him.
The official investigation into the case was initially unsuccessful and was discontinued.
Then his employer at the time, Innogy, offered a 100,000 euro reward for information that would help clarify the case.
Günther also commissioned private investigators.
A 42-year-old Belgian whose DNA was found at the crime scene has to answer in court.
However, the man vehemently denies having anything to do with the crime.
A glove with his DNA was stolen from him and then placed at the crime scene as a false lead.
If convicted, the accused faces between 3 and 15 years in prison for intentionally causing serious bodily harm.
dpa
