Computers were taken that apparently helped spread the malware.
ZD Net explains:
Ukrainian police have arrested an individual accused of spreading the Petya malware, used in a cyberattack that knocked thousands of companies offline earlier this year.
An unnamed 51-year-old from the southern city of Nikopol was detained by the state cyber-police earlier this week after a raid was carried out at the alleged attacker's home.
In a brief statement (translated for ZDNet), police say they seized computers that were used to spread the malware in the cyberattack.
The statement said that the person of interest told police he had uploaded the malware to a file-sharing account and shared a link on his blog with instructions on how to launch the malware.