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When Jean-Louis Bruguiere first investigated Paris massacre suspect Cherif Kouachi, the young man was part of a dangerous terrorist recruiting cell but didn’t strike the then-counterterrorism judge as particularly menacing.

Over the last 10 years, Kouachi found his way from the judge’s interrogation room to prison and then out — where he plotted and executed the deadly attack this week on the offices of satirical French magazine Charlie Hebdo, leaving 12 people dead and a nation reeling.

Cherif Kouachi, 32, and his brother, Said Kouachi, 34, who helped carry out the massacre, were killed Friday during a police standoff.

Bruguiere arrested and charged the younger Kouachi in 2006 for his role in a terror cell recruiting and funneling jihadis to Iraq.

“At that time, I had no impressions that the guy was especially dangerous,” Bruguiere said. “I had interrogated him many times.”

Describing Kouachi as more of a petty criminal than a terrorist mastermind, Brugiere said he was not hugely memorable because he had a “very low profile.”

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“He was very, very against the Jews,” Bruguiere said. “That I remember.”

Kouachi was sentenced to prison — and it was there that he became more radicalized, according to Bruguiere.

“In prison ... it’s very difficult to separate people,” Bruguiere explained. “So he had many contacts with many Islamic and radical people connected to al Qaeda.”

Prison — a later stint in 2010 — is also where Kouachi met Ahmedy Coulibaly, who authorities say shot dead a police woman in Paris’s neighborhood of Montrouge on Thursday, just one day after the attack on Charlie Hebdo. Coulibaly then on Friday walked into a kosher supermarket and held numerous hostages, killing four, while his former jailmate was locked in a standoff with police 25 miles away.

French authorities have said the attacks were linked: During his standoff, Coulibaly apparently threatened to kill hostages if security forces also raided Kouachi’s location. Cherif Kouachi’s wife also confirmed to officials that her husband and Coulibaly were very close.

Kouachi died in a hail of gunfire with security forces in northeast France, and Coulibaly too was killed in a barrage of bullets as police stormed the supermarket he was holed up in within minutes of the assault on Kouachi’s hiding place.

The gunmen’s wives themselves appeared to have close links as well, which is why police now are desperately searching for Coulibaly’s alleged accomplice and common-law wife, Hayat Boumeddiene.

She was first named a wanted woman by French police on Friday — described as “armed and dangerous” — in connection with the death of the female police officer in Paris.

In addition to the headshot photo released by French police, images have been released in French media purporting to show a fully-veiled Boumeddiene aiming a crossbow in what was described as a training session.

Now that Coulibaly and the Kouachi brothers are dead, finding Boumeddiene is the priority along with securing France. Officials have issued subsequent appeals for information on her whereabouts and urged her to turn herself in.

“At that time I had no impressions that the guy was especially dangerous. I had interrogated him many times.”

How involved Boumeddiene was in the attacks is not immediately clear. Police described her as an accomplice to the Montrouge policewoman’s shooting, but there was no sign of Boumeddiene in the kosher supermarket where four hostages and Coulibaly died. Still, the Paris prosecutor said police had intercepted 500 phone calls between Boumeddiene and the wife of Cherif Kouachi last month.

Many in Paris are fearful that she could mount her own attack — which, given her newfound status as the widow of a so-called martyr, could be highly likely, according to Bruguiere.

“Widows are dangerous,” he said.

“Because she is a widow of a martyr, she is very dangerous because she has to follow,” he added. “Perhaps she prefers to be killed than alive. What is much more important to achieve is the martyrdom.”