BRUSSELS (Reuters) - The cooperation between the Maltese police and Europol on the investigation into the murder of a journalist on the island has “some room for improvement”, the European Union’s security agency said in a letter addressed to an EU lawmaker.

FILE PHOTO: Maltese investigative journalist Daphne Caruana Galizia poses outside the Libyan Embassy in Balzan, Malta April 6, 2011. REUTERS/Darrin Zammit Lupi/File Photo

Maltese journalist and anti-corruption campaigner Daphne Caruana Galizia was killed by a car bomb last October near her house. Maltese authorities have charged three men with carrying out the murder but have not identified those who ordered it.

Europol has been involved in the investigation since its beginning after a request from Maltese authorities.

“While we continue to work closely with the Maltese authorities, there is some room for improvement in this cooperation and we are actively seeking to address it,” the agency’s outgoing director Rob Wainwright wrote in a letter dated April 26 and seen by Reuters.

Wainwright wrote that the investigation was “highly complex” and involved “a number of EU Member States”.

“New concerns have arisen which are now the subject of further, high-priority investigation by Europol,” he added in the letter, without providing further details.

A spokesman for Europol declined to comment. “What can be said was said by Director Wainwright,” the spokesman told Reuters.

A spokesperson for the Maltese government said: “Malta is cooperating with Europol at every level to get to the bottom of this case. If there is room for improvement, we will make any improvements necessary.”

An EU official said Europol had some concerns about the degree of cooperation it was getting from the Maltese authorities and that, as the investigation proceeded, it was raising more such questions.

The letter was sent to EU Socialist lawmaker Ana Gomes, who chairs a delegation of the European Parliament to investigate the rule of law and money laundering in Malta.

She was not immediately available for comment.

Europol's move came as a group of local and international media groups, including Reuters, began following up stories covered by Caruana Galizia, in an initiative called the Daphne Project (reut.rs/2EYpxlB).