There is mounting evidence that the intelligence services of France and several other countries were actively tracking the two brothers named as the gunmen who carried out the massacre at the editorial offices of Charlie Hebdo Wednesday.

These facts raise more and more questions about how such high-profile suspects could obtain weapons and prepare what appears to have a been a highly organized and professional military assault.

According to a report in Le Figaro, French Interior Minister Cazeneuve said Thursday that the suspects were “probably followed” prior to the shooting and that there had been no signs of an impending attack. The two brothers have been known to French authorities for at least a decade.

Cherif Kouachi was arrested in 2005 on charges of conspiracy to travel to Iraq to join the Islamic fundamentalist group led by Abu Musab al-Zarqawi. He was eventually tried and convicted in 2008, but was sentenced to only three years, essentially time served, and released.

The legal outcome raises questions, to say the least, about the reason for such leniency after a lengthy proceeding, which suggests an effort to recruit the prisoner as an informant or agent.

In 2010, according to the BBC, both Cherif and Said Kouachi were named in connection with a jailbreak plot for an imprisoned Islamist and called in for interrogation, but no prosecution was brought.

Both CNN and NBC, citing unnamed US officials, have reported that Said Kouachi had travelled to Yemen in 2011 “on behalf of the al Qaeda affiliate there” and received weapons training from Al Qaeda in the Arabian Peninsula (AQAP).

Several US media outlets reported that both Cherif and Said Kouachi had been placed on the American no-fly list many years ago and so were banned from boarding aircraft bound for or leaving the United States.