Carl Court/Getty Images Belgian police aborted Abdeslam investigation months before Paris attacks, media report Anti-terrorism unit could not follow up on the information because it was understaffed.

Belgian police received a tip-off about contact between terror suspects Abdelhamid Abaaoud and Brahim and Salah Abdeslam in February 2015 in the wake of the Verviers anti-terrorism operations, but didn't conclude their investigation, Belgian media reports.

The anti-terrorism unit of the federal police shelved the investigation because the unit was understaffed, broadcaster RTBF reports, citing a confidential report into the attacks.

Several days after police raided houses in Verviers in Belgium in January 2015 to dismantle a terrorist cell of which Abaaoud was the alleged mastermind, a source informed police in the Brussels neighborhood of Molenbeek about a connection between Abaaoud and the Abdeslam brothers. Nine months later, the brothers would play a key role in the Paris terror attacks.

The informant passed on information about Brahim Abdeslam calling his brother Salah from the Turkish-Syrian border and provided Salah's mobile phone number, according to RTBF.

Police then issued an arrest warrant for the brothers. Brahim was arrested in February, and Salah turned himself in, declaring that he had not been in touch with Abaaoud for three years.

A case file was then passed on to the federal police, where an anti-terror unit started a preliminary investigation, but decided to put the information “on hold” due to the lack of manpower to investigate the phone calls. The brothers were subsequently released. The police unit was dealing with more than 110 files and monitored 420 suspects, RTFB reports.

The federal police sent the files to a magistrate, where they remained untouched for four months, after which the magistrate decided to shelve the case.

Belgian media also reports Salah Abdeslam posted pictures of himself posing with the Islamic State flag on Facebook three weeks before the November Paris attacks. The OCAM, the coordination body for threat analysis, knew about the posts, but didn't act on it.