Greek police have arrested five people in the case of murdered University of California, Berkeley professor Przemyslaw Jeziorski, including his ex-wife and her current partner.

Arrest warrants were issued for the five suspects after they were brought in for questioning.

The Polish professor was killed on 4 July while visiting Athens to see his children and attend a family custody hearing.

According to ERT, the five people are expected to testify in front of a prosecutor on Thursday morning local time.

ERT reported that the arrests include two Greek nationals (the ex-wife of the victim and her current partner), along with two Albanians and one Bulgarian.

Jeziorski, an economist and professor of marketing at UC Berkeley’s Haas School of Business, was shot numerous times at close range near his ex-wife’s home in Agia Paraskevi and died at the scene, according to police.

A masked gunman “approached the victim on foot and opened fire from close range” at about 4.15 pm, hitting the victim in the neck and chest, according to police spokesperson Konstantina Dimoglidou.

Seven bullet casings from a 9mm calibre firearm were found at the scene, police said.

Eyewitnesses described seeing a masked man in black who approached the victim on foot, with one telling local media that she heard about six shots and saw the perpetrator run from the scene.

The shooting happened one day after the father-of-two attended a custody court hearing, police said.

According to CNN, a senior police source, speaking on condition of anonymity as they were not authorized to discuss the case publicly, previously told them that “all scenarios are being examined including close family members” and that the murder “bore signs of a contract killing.”

Police said Jeziorski had no criminal record in Greece.

Jeziorski’s family started an online fundraiser to bring his remains to his native Poland and pay for legal representation in Greece.

“He was the victim of a terrible crime, and the perpetrator is still at large. Our family is heartbroken, and we are doing everything we can to ensure that justice is served,” Jeziorski’s brother Łukasz wrote on the fundraising page.

The dean of UC Berkeley’s business school, Jenny Chatman, said she was “heartbroken” by the death of Jeziorski, who she described as a “beloved member of our marketing faculty.”