EU heads of state did not discuss the Daphne Caruana Galizia murder investigation during a two-day meeting held on Thursday and Friday, EU Council president Charles Michel told journalists.
Mr Michel said that he did not want any political interference in what was still an active case.
“At the moment inquiries are ongoing,” Mr Michel told journalists during a closing news conference after what is likely to be Dr Muscat's last EU Council meeting.
“They must be based on the rule of law and it is very logical that we didn’t speak about this topic. I do not want to have any interference in this inquiry,” he said.
He described Ms Caruana Galizia’s October 2017 as "a serious attack" on the freedom of the press but also a “human drama” and said he would continue to be in contact with Ms Caruana Galizia’s family and “will go to Malta”.
EU heads of state including Dr Muscat met in Brussels on Thursday and Friday just as British voters went to the polls, and discussions about Brexit played a major part in the meeting agenda hours after Boris Johnson’s Conservatives electoral victory.
European Commission president Ursula von der Leyen warned of the tight timing for securing a trade deal with Britain.
"The time frame ahead of us is very challenging," von der Leyen said, following a discussion by EU leaders on the way forward after Brexit, now expected on January 31.
On the "first of February, we go to work," she said.