An 18-year-old man has been detained on suspicion of killing a former Ukrainian lawmaker, local authorities say, after her fatal shooting in the city of Lviv.

Iryna Farion, 60, died in hospital last Friday after she was shot in western Ukraine, the mayor of Lviv, Andriy Sadoviy, posted on Facebook.

A specialist team of Ukrainian security forces and criminal analysts tracked down the suspect on Thursday after 139 hours of investigative work, according to the country’s Interior Minister Ihor Klymenko. Authorities scoured about 100 hectares of forest and identified him using surveillance cameras, the minister said.

“We checked every corner of the shooter’s escape route,” Klymenko posted on Telegram. “Identifying and detaining the offender was a laborious process that required the highest professionalism, endurance and discipline to avoid making any mistakes. I thank the entire team.”

Ukrainian President Volodymyr Zelensky praised his country’s security forces.

“I am grateful to each and every one of them who added more facts to the picture of the crime every day and brought the full truth closer,” he said in a post on Telegram on Thursday.

A former nationalist parliamentarian and professor, Farion was known for her unfavorable attitude towards the Russian language, which is spoken in eastern Ukraine.

The Security Service of Ukraine launched a criminal investigation against the academic last year, after she published a social media post with a screenshot of a message from a pro-Ukrainian student in occupied Crimea, containing the name, surname and other personal data of the sender. That information became the basis for his persecution by the Russian special services.

During the investigation in November, Farion told authorities that she categorically rejected Russian-speaking members of the Armed Forces fighting against Russia’s full-scale invasion, according to Reuters, saying she could not call them Ukrainians.

Her statement triggered a wave of outrage among sections of Ukrainian society.